Of course, it helps to "explain" the tip, especially if it isn't a whole dollar or American Eagle. (if your bill is that high)
Because they only have to "claim" face value!!!!
And they can pay the tax on it with FRNS!
Odds are, yours will be the only tip like this they receive, but it will be a small gesture that can educate many, not make you an ass, and you're doing them a favor.
On top of it, they might be inclined to try to save it since it would be foolish to spend it or change it out.
I know if I ever got a silver tip (it happened once or twice) I did manage to save it, instead of drink it right after the shift along with the FRNs I just made.