When we were at CHA there were so many of us we were constantly trying to find eachother in the crowd. Finally someone (I can't remember who) suggested we make this obnoxious lound noise that sounds sort of like blblblblblbl. When we'd hear it we'd stop dead in our tracks and know that someone from our group had spotted us and wanted our attention. It ended up being pretty funny after awhile.
And now it's the official MFT greeting!