Marius, assisted by Razvan, can automatically tell that the substance is blood ... or at least primarily blood. Marius can take some scratched into a vial of his alchemy crafting kit for later study. However, he knows that he doesn't have the means to study it himself (an alchemy crafting kit won't do it), meaning he will have to ask Mr. Evans to do so with his laboratory, or to get permission to use that laboratory.

Given what Abrax said ....
Wren casts detect magic, the first proof of any magical skill from him. When people look at him he just shakes his head, backing up what Abrax said.

Zauberei, assisted by Marius, can look at the Blood-V more carefully than Abrax. Together, they deduce because of the downward pull from upper left to lower right that the dominant hand of the vandal is right-handed. Which narrows down nothing, given hat 85% of the population is right-handed.