A brief glimpse of whatever humanity is still in Frank Castle.
He lost his family, a wife, daughter, and son, in many ways he lost more than just the ones he loved. He lost himself.
The toy gun represents more than just a memory, it represents the dream, the shadow of his former self as a family man, a loving father and husband. That’s what it gives to him, an honest representation of the monster he’s become.
Castle claims to “use it” sometimes. How exactly does he use it? Pretending to be his own son, or to be playing with his son, fighting off the imaginary bad guys, the aliens, the monsters? The gun gives him a flash of his past and “what could have been” and maybe it causes a shift in personality, in that he has built another personality: that of the father he was, in order to play with the gun. Either playing the part of father or even his own son and giving himself some excerpt of solace.
Perhaps he doesn’t, sure Frank Castle is a messed up individual with a lot–a lot–of issues but an ongoing split personality? Maybe, maybe not. I like to think that when he uses it the Punisher is on the prowl, driving around, leaping from building to building, maybe even sitting the bushes planning an attack. He’s watching the comings and goings of guards and thugs alike, then as he plans his attack he pulls out the small toy gun, aims it at the bad guys and makes a “Bang! Bang!” sounds to himself. Living, just for a brief second, as a child. A careless figure, a respite from the horror of being The Punisher.
The gun represents so much for the Punisher, that it’s difficult to decipher. It’s just another degree of the madness of Frank Castle. A loving father descended into pain and psychopathy, yet being almost well adjusted…well, in addition to the slaughtering of criminals and stuff.