The laundry mark is an ID stamp used by the soldiers to identify thier stuff and mark it individually as thiers. The laundry is done in bulk, so there are a lot of uniforms mixed together. Not to mention, if you have severl individuals with the same last name. The Laundry mark, therefore, identifies this as to which soldier. So Pvt. John Smith with a hat size of 7 1/2, shirt of 14X32, and pants of 32X34 doesn't get Pvt Ray Smith's stuff which is a 6 3/4 hat, a 15 1/2X34 shirt, and 31X34 pants. Since both would have different serial numbers, it makes it easier to identify. The reason ou would see it on web gear and helmets is because the soldier is responsible for his own stuff, so if it gets stolen, it can be proved it's his and if he loses it and his drill instructor, platoon sargeant, officer, etc. can identify who it belongs to. Also, if a thief is caught, they can identify who he stole the gear from. It's a very common thing to see on WW2 and Korean War stuff.
By the way, the US disc on the side looks modern and wasn't worn there normally anyways, so you might want to remove it. It's for the collar of khaki shirts and the dress jackets.