On a visit to NYC last week, I noticed that some restaurants are trying another scam. It seems that they are trying to get some extra money out of foreigners who are not fluent in English.
When the bill comes, it will say (example):

Food and beverages $ 100
Gratuity 20% $ 20
Total $ 120

Followed by (in BIG BOLD LETTERS)

SUGGESTED TIP:
15% $ 18
18% $ 21.60
20% $ 24

Many foreigners will not know the word "gratuity" but will have heard about "tip" and the general practice in the US to add 15 - 20%. By presenting the bill in the way described above, they are basically trying to scam the innocent visitor for a double tip.