Look just in front of the bottom of the trigger guard, behind the ramrod's pivot point. There should be a two-letter mark there ("AP" on mine.) The link Prairie Dawg provided has a list of those marks. However, it shows mine as being made in 1986, two years after I purchased it, so I don't know how accurate the chart is.
These are, as indicated, not worth much. They are fully serviceable and useable, but were manufactured in huge quantities, imported, and not quite as refined as those from some other makers. The brass frames are not as rugged as the steel ones so, if you shoot it, don't load it up to "mega" power charge levels.
I purchased mine in 1984 from a pawn shop, and I was eighteen years old. I think I paid around $125 or so. I had every intention of shooting it, but got intimidated by the "complexities" of its operation and post-shooting cleaning routine, so I never did. In 2009, I finally went out and bought "the fixin's" to shoot it (powder, balls, flask, primers), but still have yet to make it to somewhere I can play with it. Having kind of "rediscovering" it lately (and talking about it now) is making me resolve to shoot it before the weather heats up.
That logo on yours is indeed different than the one on mine, but I don't know which logo is the newer one.