Recall the output of the kill -l (l for list) command; the platform's supported signals are displayed—numeric integer and symbolic name, both. The first 31 signals are the standard or Unix signals (seen in Chapter 11, Signaling - Part I, The standard or Unix signals section); we have been working with them quite a bit now. 

Signal numbers 34 to 64 all start with SIGRT—SIGRTMIN to SIGRTMAX—they are called the real time signals:

$ kill -l |grep "SIGRT"
31)SIGSYS      34) SIGRTMIN    35) SIGRTMIN+1  36) SIGRTMIN+2  37) SIGRTMIN+3
38)SIGRTMIN+4  39) SIGRTMIN+5  40) SIGRTMIN+6  41) SIGRTMIN+7  42) SIGRTMIN+8
43)SIGRTMIN+9  44) SIGRTMIN+10 45) SIGRTMIN+11 46) SIGRTMIN+12 47) SIGRTMIN+13
48)SIGRTMIN+14 49) SIGRTMIN+15 50) SIGRTMAX-14 51) SIGRTMAX-13 52) SIGRTMAX-12
53) SIGRTMAX-11 54) SIGRTMAX-10 55) SIGRTMAX-9 56) SIGRTMAX-8 57) SIGRTMAX-7
58) SIGRTMAX-6  59) SIGRTMAX-5  60) SIGRTMAX-4 61) SIGRTMAX-3 62) SIGRTMAX-2
63) SIGRTMAX-1  64) SIGRTMAX 
$ 

(The first one, SIGSYS seen here is not a real time signal; it shows up because it's in the same line as the other SIGRT's and so grep(1) prints it.)