very easy way to tell is how the light comes thru it behind a light bulb every color should be bright also the backside should have some light shelving were the lettering or the graphics are i have also found that the backsides should almost look white washed with typically a white color, slightly covering the colors that it displays. this is the easiest way that i can tell. and of course if its numbered or signed good way but then again they are making repop of pam and telechron clocks that are signed with pam and telechron clock co logos just like originals.
