Tip included in the check - US style

There are a number of places in the USA where it is common for the tip to be already included in the check. Miami beach, Orlando, and sometimes New York City, among others. I point this out because I have encountered a number who live in the USA who say it never happens there. Yes, these are places frequented by visitors from overseas, although even there my experience is that those from the US are still in the majority.

However, the credit card slip/machine is still invariably presented with an open line for "tip". Would it be ungallant to say that they hope you haven't noticed it is already in there ? Just to aid the understanding, the check for the already-added amount is often labelled with useful abbreviations such as SV CH or similar.

I was once told, when I questioned a manager about this, that it was "in case you received the best service of your life". I had to inform him that, on the occasion this does happen, it is exceedingly unlikely to be in Miami Beach ......