How do I describe the smell of blood dried for 1 day or more?

[Lupine]

I'm doing a mystery campaign, and there will be some clues that they can use to help find the perpetrator, and I want to hint to those clues, but I don't want to give it away to them straight up.Thus for them to find the blood trail, I want to describe the smell of dried blood such that they can recognize it and try to find the source of the scent.
The scene is in a noble girl's room, and she has been kidnapped, though she fought. She is a studious elf with a love for organization and reading. She hates the cold and blood.
Some Guidelines:
Please do not use blood or anything directly relating to it, it defeats the point
Please stay away from cliches (everyone knows sickly sweet and metallic. I don't want to use them because it also defeats the point. I want the characters to think "What's that smell?"
Please don't give me editorials as to whether or not this is a good idea. As a DM who knows his group really well, I have already decided what will be fun for my group (though if you have some fun ideas for certain clues, by all mean, give them to me)
Thank you in advance!

[Ganymede]

It smells like your sword after an adventure if you forget to wash it?

I don't get why you're playing Hide the Ball with a smell the PCs will recognize, with or without a skill check.

[ProsecutorGodot]

The only real difference between fresh blood and dried blood is how difficult it would be to notice it. It's going to smell about the same. Metallic, slightly earthy.

The best I can come up with considering how you've taken away the option of using the most accurate descriptor is "You smell something faintly familiar, you're not sure what exactly." If you've had them roll perception (or investigation) and their roll is what you would consider high enough, you could also add "it seems out of place, not something you'd expect to smell in a home"

And regardless of your wishes otherwise, I feel the need to point out that the smell of blood should be incredibly obvious to an adventurer. Trying to make it a mystery isn't worth the trouble in my opinion.

[CorporateSlave]

I'm doing a mystery campaign, and there will be some clues that they can use to help find the perpetrator, and I want to hint to those clues, but I don't want to give it away to them straight up.Thus for them to find the blood trail, I want to describe the smell of dried blood such that they can recognize it and try to find the source of the scent.
The scene is in a noble girl's room, and she has been kidnapped, though she fought. She is a studious elf with a love for organization and reading. She hates the cold and blood.
Some Guidelines:
Please do not use blood or anything directly relating to it, it defeats the point
Please stay away from cliches (everyone knows sickly sweet and metallic. I don't want to use them because it also defeats the point. I want the characters to think "What's that smell?"
Please don't give me editorials as to whether or not this is a good idea. As a DM who knows his group really well, I have already decided what will be fun for my group (though if you have some fun ideas for certain clues, by all mean, give them to me)
Thank you in advance!

Well since you've discounted the cliches (which are such because that's what blood smells like), you may want to move into metaphors or riddles. Like describe a faint smell that is somehow vaguely familiar, yet also somehow something just unusual enough you can't quite put a finger on it... then have them try to search for the source to identify it? Any descriptor that actually fits blood accurately is probably going to be a dead giveaway.

It's not unreasonable that an adventuring party in a fantasy setting would be accustomed to the smell of fresh blood (from all the fighting injuries)(, as well as badly decayed bodies, but the fading scent of day old and dried blood might not be that common of an occurrence in a world where healing (and cleaning!) magic makes blood tend to either be freshly spilled, or found associated with old corpses where the smell of the rot overpowers the smell of the dried blood.

I really think you're going to need to stay very vague or they're going to be "oh, blood." instantly.

[Lunali]

Unless the adventurers have unusual senses of smell, if there's enough blood that they can smell it even after it's dried, there's enough blood that they'll probably see the trail before they smell it.

[Lupine]

Thank you for the help, I totally forgot that they would've known the smell of long dried blood. ProsecutorGodot's answer is of the most use to me.

In response to Lunali, having had more bloody noses than I care to admit, I know the smell of fresh blood extremely well. It is extremely pungent, but I always take care to wash it off any surfaces long before it dries (Because ew. blood is disgusting). I was mostly asking if the scent of blood changes in pungency or scent.

Sorry for not being clearer

Also my players are obsessively attached to the "Don't tell us directly" mentality. They like figuring out things with little more than raw sensory data.

[Ganymede]

They like figuring out things with little more than raw sensory data.

Unless you are prepared to hand them something covered in dried blood and have them sniff it with their eyes closed, you can't really do this. Then again, scent-based handouts could be a thing in the next Beadle & Grimm deluxe set.

[SleepIncarnate]

Unless you are prepared to hand them something covered in dried blood and have them sniff it with their eyes closed, you can't really do this. Then again, scent-based handouts could be a thing in the next Beadle & Grimm deluxe set.

This is a thing you should totally do. Get some pig or cow blood from a local butcher shop and get a rag that's been dipped in it and let dry for a couple days.

[Lupine]

This is a thing you should totally do. Get some pig or cow blood from a local butcher shop and get a rag that's been dipped in it and let dry for a couple days.

I actually get semi-regular bloody noses, I could also probably just use my own... Both options would probably gross them out.

[Tvtyrant]

Depends on what type of blood it is and whose blood it is. Deer and dogs are so pungent it takes days to fade, human blood is relatively subtle by comparison. Bird and fish blood is even less noticeable, I can gut a duck or white fish and not be bothered but I would never take an unbled mammal carcass into my house.

I would have them notice a faint hint of copper in the air, and brown dust flaking from brown paint.

[Honest Tiefling]

I don't think dried humanoid blood would have much of a smell. Also, would it overpower other smells present in the room? Presumably she has a fireplace or something for heat, since she hates the cold. Perfumes, flowers, incense, inks and those thingys you put into clothes to make them smell good are probably going to throw off the scent as it were.

But she's not really a human, is she? Does elven blood in this setting have different properties than human blood? This would be a vital clue as it would be HER blood (or well, of any elf) not someone else's.

[Zaharra]

It smells earthy with a metallic tang, and possibly with a musty smell if it's enough blood and bacteria.

Personally I can pick up that I'm smelling blood pretty quickly, but I guess if you want to keep it to "An earthy scent, undercut with a metallic tang permeates the room, sourceless but seemingly familiar." Or something similar that could maybe work?