A lot of folks don’t list a PPC address in their signatures - everyone should! Sometimes one might want to tip another person and can’t easily without that 
Already did it a while ago! 
Honestly it comes off sort of spammy to me when I see a bunch of addresses in a signature. That kind of thing turned me off when I was first perusing the Bitcoin forum trying to learn about cryptocurrency.
It is a social lubricant for working with lots of strangers who want to remain anonymous. Much easier to pull addresses from signatures than send a pm asking for an address and wait for a response. Never know who will sign back in when etc.
How many times have you ever been tipped?
I help people trouble shoot tech problems in chat and with volunpeer activities so I have been tipped. I changed the address at the start of this month to help with anonymity otherwise I’d tell you to put it in block explorer to see for yourself haha. You don’t have to list an address if you don’t want to but you’ll be happy if you do
i do that too sometimes, shamelessly hoping for a tip, but it hasn’t happened yet lol