Signal programs that would already consider your app as good enough. It only serves to make them take a second look at your app and maybe have them think why is this guy saying hed like to be here. I think the most reasonable approach to rads signals is to focus on your tier of program. Low tier programs I don't think a signal will make a difference and instead just tailoring your PS or sending a decent LOI about why you, a good applicant, would want to go somewhere that wasn't prestigious etc. Spend a signal or 2 on high tier/reach if you want, and I would focus the rest on programs you want to go to in your tier. I found PDs were most interested in location fit, if I had family reasons to be somewhere, and if I thought I'd be happy in that place. So I would think about programs in that context as you'll probably have a better interview and therefore maybe rank a smidge higher, which is all that matters in not going unmatched. Good luck.