If you're at a farmers market or Caltrain station on the Peninsula in the coming weeks, don't be surprised if someone asks for your signature. In the face of looming deadlines, tenant advocates in Mountain View, San Mateo and Burlingame are gathering signatures to get rent control initiatives placed on their November ballots. In interviews on Friday, initiative backers from the three cities expressed varying levels of confidence about their prospects of gathering the number of needed signatures…