Convert *signed* EBCDIC to packed decimal

[Doug Wegscheid]

I'm getting reacquanted with s/370 assembler after a 40 years hiatus.
I'm working through some examples from my Kacmar book, and need to convert from 
a character string to a packed decimal. PACK almost works, except it does not 
handle a leading (or any) plus or minus signed.
Is there a *simple* way to do, or am I going to have to scan for the sign 
characters myself, remove them, pack the result, and flip the sign if it was 
negative?
Alternatively, is there some accessible prior art out there?