Blood Type on Boots Question

I have a pair of Altama desert boots dated 1997. On the outside heels, there is an O+ written in Sharpie. I know it is the blood type of the soldier whom the boots belonged to before coming into my collection. What I'm wondering is, if this was a common practice in the US military while someone was deployed to Afghanistan or Iraq? Thanks in advance for any help.
Arch

I'm sure it is common for Special Operation units. Remember in Black Hawk Down, Delta Force operators duct taped their boots with blood types.

My only pair of DCU boots have blood types on them...I never gave it another thought...
Andrew

Thanks for the great info guys (especially the PM I received from an anonymous member ). I found what I needed to know!
Arch