In game, there are some different squad-specific buildings such as ampulomet, high-caliber machinegun and etc. Therefore, I suggest some variants of recon squad specific building (you can add one or more, idk):
1) Periscope.
Sandbags with a periscope behind that peaks above them:
Mechanics: A player can “seat in” periscope and he can look in 120-140 degree horizontally and 60 degree vertically up and down. He can magnify in one or two magnifications, he can mark enemies. Periscope marks are visible a little differently than regular player mark and they stay on objects for much longer time - 3x times longer.
Additionally, you can add a distance to periscope marks. It shows the distance from the mark to every player. Can be useful for anti-tank bazookas and such.
2) Camo net.
Camouflage net that can be built in two variants: Camo “roof” that hides an object from above or Camo “wall”:
Mechanics: A player can build a camo net to hide something, for example - sandbags with a rally point behind or machinegun nest. A net is half-transparent from one side and fully opaque from another. Therefore you can shoot and look from behind the camo net. Camo net is fully bullet-transparent, any projectile can fly thorough it freely, but it has very small HP and can be easilly destroyed by explosion.
Additionally, there can be different camo net variants for different maps. Yellow one for sand dunes, green one for forests, camo net with grass for fields and a grey one for cities.
3) Reconnaissance station.
A building thats looks kinda similar to a rally point. But its larger and higher.
No photo, you have to imagine it.
Mechanics: A player can build that station and it will mark enemies, once a minute or less, under open sky in a range around it. Those marks look differently than regular player marks and they dont follow objects/tanks. They are stationary. You can make it so it checks if a station can see an object or not, idk. You can increase its range by building it on higher point. On a rooftop or a watchtower. It passively emits a silent sound and also, when marking, it emits a much louder sound that can tell an enemy that somewhere near there is a recon station, on a rooftop or somewhere else.
A little passive reconnaissance, why not.