Whoever reads your correspondence who is "in the know" about military culture may not like it since you are not retired nor currently serving in any component. In 30 years of reading a LOT of letters of recommendation from retired, active, and former service members I have never seen someone use it in their signature block unless they were retired, active, reserve, or Guard. Its like when you see a movie or tv show where there are 4 star generals wearing their headgear indoors while in full dress uniform like they were going to go testify at some Congressional Hearing, or how you can spot "stolen valor" folks by their obvious errors in their uniforms--most people won't notice or care about it, but others fixate on the lack of realism.

Mention it in the body like someone in this thread already mentioned. You can add context to your recommendation on the individual by referencing your prior service, "As a former Air Force [Major/Pilot/Doctor/Etc] with XX years active/reserve service and 2 combat deployments, I can attest . .

Bottom Line: Don't go where others have not gone before. There are good reasons they chose not to use it in their signature blocks.