Have you ever seen this:

Flew FRA-HAM today in A310 and used the aft lavatory. there was an empty alumin LH meal dish sticked with an LH label to the mirror. The label said "DANKE" (thank you) and it was a clear invitation to passengers to leave tips for the crew there.

After having returned to my seat I thought maybe I was wrong and they were collecting money for the victims of the flood in Germany in a very unconventional way and there would be some sort of annoucement during the flight but it was not.