Just like the error codes (EPERM, EEXIST, etc), signal numbers are different on different platforms. EG on macos, SIGCONT is 19; on Linux SIGSTOP is 19. Big difference.
If you have PCNTL compiled in, you can use the constants like SIGCONT; i trust they're all correct.
If not, look in /usr/include/signal.h; these days its tons of ifdef mumbo jumbo but you can go to /usr/include/bits or /usr/include/sys or something and look for files named sig*.h; one of them will list them for you.