Distinguish between Signal type - SIGUSR1 vs SIGUSR2

I have a main in which 2 signals SIGUSR1 & SIGUSR2 are being sent using kill() to children pid1 and pid2. The signals are sent one after the other:

kill(pid1, SIGUSR1);
kill(pid2, SIGUSR2);

Using code below does not work:

 signal(SIGUSR1, handler);
 signal(SIGUSR2, handler);

How can I distinguish which signal was generated in pid1 and pid2?

Thanks.