Bloodstains are fabric paint (well, acrylic + fabric medium), reagent is four opened glow sticks and an equal amount of dish soap, pulled into the syringe and then sealed with hot glue. (Note: the glow sticks I had were labeled as non-toxic, just with warnings about staining. Turns out the little breaky bit is made of glass, pretty sure that’s why my parents warned me not to do the thing I just did.)
Pros: reagent actually glowed and looked super cool (especially outside/in poorly lit rooms)
Cons: can’t use the syringe again, reagent separated over time into glowy goo at the bottom and pale watery liquid at the top, glow only lasted for four hours.
Got recognized by a couple of people (and mis-attributed by a couple more, because there’s ten tons of white guy characters with white shirt, black tie, glasses, bloodstains, and a menacing expression). Would totally do again, possibly with further trials with reagent fluid (keeping it safe from leaking as well as reusable is the trick, although the syringes are like two bucks, so it’s not much of a loss).