Non-Magical until....

[KyleG]

Can you have an object be non magical (so that the PC might think its just a trinket) until such time as its in the presence of a certain magic and THEN its magical affect activates/can be identified?

[rferries]

In 3.5, magic aura (http://www.d20srd.org/srd/spells/magicAura.htm) might be precisely what you're looking for. Otherwise certainly, an artifact or magic item might be crafted with such a quality.