I often ask at the bar for 2 glasses of tap water, then point out to everyone that this barmaid has been giving me free drinks all night

If I'm feeling self-conscious about flying solo I will get a tap water and a red bull so it can be construed that I'm buying one for someone else. I also sometimes use the 2-drinks thing when I want a break... sit at a table with the second one opposite me at an empty seat, looks like I'm waiting for someone to come back.

On very rare occasions I have had women approach the table and sat down in the empty seat to "steal" me from the unseen (and non-existent) competition!