If you only need two signals, stick with USR1 and USR2; that is what they were designed for, after all. Picking any other (defined) signal will confuse either the User or the Maintainer on down the line, unless you are very clear in the documentation of your non-standard use of signal 'Foo'.
I'd really stay away from 'make up two of my own...' It's almost a non-bet that if you have someone else in the shop who 'needs' to define their own signal, above SIGRTMAX, they will pick a number you are already using. Sorting out a collision-bug like that is always fun....
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I Go Back to Sleep, Now.
OGB