I'd guess this plaque was awarded to the lifetime employee of some business or corporation to mark four decades of service, and then perhaps displayed on the wall behind his or her desk along with--or replacing--other plaques marking 5, 10, 20 and 30 years of the same! At this point though it could certainly be mark  40 years of marriage or life itself, a perfect gift!

Cast brass I believe and in good shape, with a little staining to the face of the big 40 (as there should be!). 6 1/2" long x 2 1/4" tall , 3/8" thick.