[Boatanchors] Dow key relay identification?

[George KB2Z]

Can anyone tell me how to tell if a  Dow key relay is isolated for tx-rx 
use? I have 2 that seem identical
DK-60 type. The DK-60 (G) isolates the rx on transmit. I have been using 
one for a long time with no problems. I got it with a pair of Halli's.  The 
second one I have looks like the one I'm using. The only marking on both is 
110v on the coil.  The casings for both are black in color. I want to use 
the second one for a tx-rx but dont know how to tell if its safe to use.
Thanks in advance, George KB2Z