AAMC's program-signaling analysis found that sending a signal was associated with a higher probability of an interview invitation in every participating specialty[1]. Because signals are scarce and can't be reallocated once submitted, how you split them across programs matters as much as how many you have.
First, confirm your specialty's current signal count and tier structure in the official ERAS materials for this season — allotments change year to year. This tool doesn't report or assume any specialty's number; enter your own below.