While driving in Pennsylvania, specifically in Schenley Park in Pittsburgh, I was merging from a side-street to a main road, as seen in the picture below. I had stopped at the stop-sign, checked for traffic, then proceeded on, whereupon a police officer started flashing his lights at me. He asked where I was coming from, and whether I'd had my turn signal on, stating that he hadn't seen one. I answered him honestly that I was coming from karaoke in Oakland, and that I had had it on, the left turn signal specifically. He did some checks on his laptop and then sent me on my way. In retrospect, since it was a little after 2 AM, he was probably randomly pulling people over, knowing that the odds were that he could find someone who was driving inebriated after leaving the closing bar, the turn signal being a flimsy excuse for probable cause. That said, it made me wonder, which turn signal should be on in this sort of situation?
One option is to have the left turn signal on, since you are merging left into traffic. On the other hand, I'd come to a complete stop, and a left turn signal might confuse people into thinking that I planned on a left turn (not feasible here, but possible in some other merging situations) and one does sort of have to turn right from the side street to get onto the main street. Reading through the PA traffic manual didn't help. Poking through the Kentucky and Ohio ones (they were convenient) didn't bring up any helpful laws for how to properly signal a merge. Is there a standard rule in Pittsburgh, in Allegheny County, in Pennsylvania, or in the United States in general, that I can rely on?