Does any FM or other manual specifically state Chain of Command call signs?

I think what you are looking for is the SOI.

The answer you seek lies in FM 3-36 The Radio Operators Handbook.

SGT Derrick Tims

I know this is old, but this is a recurring question in various quarters.

This is just an accepted (and a poor, in my opinion) tradition.

What we usually refer to as Callsigns are really Callwords. A proper callsign is a letter-number-letter combination then followed by the usual suffixes and expanders.

Callsigns, callwords, suffixes, and expanders, are all subject to change and there are no special rules for what they have to be. Common sense applies--don't violate other rules to do it like using a person's name as a callword and don't confuse people by trying to use an established proword or phonetic alphabet word as a callword (Wilco 6 this is Lima 9....).

There was a time when by doctrine callsigns, frequencies, suffixes and expanders all changed every 24 hours. Our technological level has made us soft in this regard and I think that's a mistake.