In a perfect world you'd pull out your S&W
model 29 and fire a shot over their heads.
Seriously though, that's is a tough situation. On the one hand you want to defend her honor so to speak as well as not come across as a girlie man. But then on the more practical and realistic side of the coin you can't overlook the fact that your hopelessly out numbered.
I actually had a similar situation where my girlfriend at the time was sunbathing on the deck when some construction workers a few houses down were whistling and what not. On the one hand it was kinda flattering but at the same time it kinda pissed me off. I seriously considered stepping out on the deck with my Springfield Armory M1A and pretend to be cleaning it in open sight. Ultimately I decided against it, she decided to just come inside and while I didn't tell her this frankly she wasn't worth going to jail over.
As for your question I'd say about the best you can do is give them a very confident and mildly menacing look
while you continue on your way.