I am not a lawyer and am not competent to give legal advice.

That said: I can only assume that you are standing so close to the problem that you can't appreciate the sheer scope of your legal peril. The odds that you have a case are not worth the legal fees to calculate. Lawyers' calculators are not optimized for small numbers. Save your money and change the name. Unless your promotional materials include a fleet of blimps.

If you do hire a trademark lawyer, your money would probably be better spent by having him or her help you with your next name. I'll do my part by suggesting a list of names you should avoid in the future:

  Sitecrosoft
  SighBM
  Sicombinator
  Sapple Computer
  Siteman Sachs
  Sintendo

Though it's a pity about the last one, which would be a great name for a site specializing in off-color Flash games.