My main concern is always the possibility of illicit drug residue.
An ex-LEO - retired but still part of the club - told me about the amount of drug residue to be found on a lot of currency, and when I asked about the possibility of this eventually getting on my wallet, he chuckled but then got thoughtful...
Anyway, when I heard about the Deming, NM drug warriors awarding free enemas to people because some semi-trained mutt thought the driver's seat was a hit, that conversation came to mind.
Mr. niteowl77