http://www.lifeprint.com/asl101/pages-signs/s/single.htm

Give the symbol for "you are single", (symbol "single, alone, somebody, something" by sticking your index finger up on right hand, other fingers closed, make a small circle. Add in the word "obviously" by sneering as you do it.

Alternatively, make the symbol for "lesbian" by keeping your fingers straight on your right hand and touching the tip of your thumb to the tip of the index finger while keeping thumb straight and showing the resultant crevice to the party concerned. (OK I made that one up!).