Sometimes GNU/Linux tools will use SIGUSR1 or SIGUSR2 for equivalent functionality. I just wish they'd wire up CTRL+T to send one of those signal and then people can actually start building software that makes use of it. Having to open another terminal just to do a kill -SIGUSR1 <pid> is insane
My understanding was that there are a limited number of signals—one for each bit in a 32-bit integer, and I recall reading that Linux chose to use that particular bit for some other purpose (SIGPWR).