This is a Hopkins & Allen five shot .38 S&W revolver. The mechanism is rather unique. The top strap has a rectangular slot which, when closed, sets down over the angled stud part of the frame rising above the breech. There are slots cut into each side of the stud and spring loaded bars recessed into each side of the top strap. Those bars are pivoted in the middle so that they snap inward and latch into the notches of the standing stud. Pressing inward on the front of those bars will pivot the rear end outward and free of the notches so that the top strap can swing upward to eject spent shells and reload.
The trigger pull is horrendous due to the design of the mechanism. The hammer pivots on an eccentric cam so that as the trigger moves rearward it not only pushes the hammer rearward but also cams it downward so that when released the top of the hammer will strike the frame mounted firing pin. When the trigger is released the powerful mainspring cams the hammer back up so that the hammer rests on the frame and not touching the firing pin.
The top strap is marked "safety Police". I think the safety refers to the fact that the trigger pull is so heavy few children could fire it.
The caliber is not marked in any way but the chambers accept the .38 S&W cartridge. The chambers are not throated at all, just bored full diameter right through and will accept a .38 special case but a loaded bullet sticks out the front.
I have acquired four of the cheap "Saturday Night Special/Two Dollar Pistol" types and find them interesting. All four have unthroated chambers and with the cylinder removed from the gun you can drop a cartridge into the front as easily as the rear.
Three of those cheap pistols are top breaks, each with it's own unique method of latching, this one I feel is rather stronger than the common S&W style. The gun is in pretty good shape overall and I think it would stand up to a great deal of use with normal .38 S&W rounds. It is not however a real fun gun to shoot. Recoil is surprisingly sharp and the very heavy trigger pull in both single and double action modes combine with the tiny sights to make it very hard to shoot with any accuracy. That is even assuming an unthroated chamber could be capable of accuracy.