If the general public had a problem with the bit of dirty ash on my tamping finger, then they would probably also have a problem with all the various other work related dirt on my 9 remaining digits, at which point I throw my hands up and declare the whole thing redundant.
The other day I was over-emphasizing something to my neighbours while stopping for a chat and thanks to my wild hand gestures (possibly contagious, my wife is Italian) I showered them both with ash from my pipe. THAT was embarrassing, I will readily admit.
Isaac.