Signal was my son's first choice and Kuwait was his first Duty Station, also his first choice.
I know this will ruffle some feathers when I say this, but Signal Corps has a reputation of being a little bit like the IT department. It doesn't get the respect of the combat arms branches, but the enlisted personnel tend to be slightly better educated and score higher on the ABSAV. Many aspire to Signal as a path to excellent job prospects in the civilian world. Since your son will be a manager, he will appreciate their motivation.
If your son is smart, motivated and in good shape he will have opportunities to broaden his experience, by attending different schools which I'm sure he will want to grab--from Airborne to Ranger. He just needs to remember that his performance as a Signal Officer will determine whether he gets those other opportunities.
That has been my son's experience mixed in with a good share of luck. He just committed for at least another 3 yrs.
If you don't mind me asking, what was your son's first choice?
I wish him all the best!