I tend to go with weapon or animal themes, with an exceptions here and there.
Skirmishers: Mostly leather armor with a metal helmet and chain shirt under the leather armor. Issued with spears because historically those and hatchets/axes were most likely to be the weapon of a commoner. Skirmishers are professional light infantry who rely on speed to take down enemies. They are glass cannons without a doubt but I've seen what lightly armored speardwarves can do to a siege.
Conscripts: When I have the time to equip a needed swarm of untrained rabble to hold something back. Survivors will probably be cycled into a Skirmisher squad. Might have the armor if they're lucky, but often it's just a spear, metal hat and a wooden shield.
Weapon and/or animal themes tend be be variable, and sometimes I use names of squads from certain LPs: Cazadores, Hammerheads, Golden Maces, Cave Dragons, Thunderous Boots (for when I have musket dwarves in masterwork,) Ironbreakers (because who doesn't like a badass Warhammer reference like that for hammerdwarves?) The Gilded Men, New Paints, Copper Gears...
Other times I'll go all military organization: 1st-5th Squads, 1st Company for the first 5 squads, 1st-5th Squads, 2nd Company for the next and so on. In those cases I only need to know who the squad leaders are to know what the squad is armed with and that's just a quick look at the military screen if I forget.
Fortress Guard tends to just be named that in most cases, plus with raw mods I also have a "Governor's Guard" and sort-of reestablished a Royal Guard squad, as well as made nobles have to earn their title and privileges through force of arms which has me generally just name them by the noble: "Urist McBaron," Urist McCount," "Urist McKing" and such.
How I keep track of this shit I have no idea.