okay, so this word is from Italian, not German.
but I used it for Friday's wwftd, and I got this from our friend Emanuela:

I never heard this word, perhaps since I don't drink wine.
It sounds a word from Tuscany, indeed.

Some comments:
1) We always eat using a tablecloth on the table, so the most likely possibility is the mark over the tablecloth (if someone says "on the table", I bet that he is meaning "covered by the tablecloth")
2) Very clearly, there is the root "culo", it means "ass", and it is a not polite word. The reason should be that the "culo" = "bottom" of the glass leaves the mark.
For this reason, I feel the word as very "popular" and not "elegant"