Mine, which I bought new around 1977, is marked on the left side of the receiver above the trigger assembly. The first line is "Remington", followed by a dot inside two concentric circles, then "Wingmaster" with a wing on the W, followed by a registered trademark symbol (R inside a circle). The second line has the serial number below the "Remington", and "Model 870 TB" below the "Wingmaster".
If you look close at the T.B. I got ok I needed to scrape some more paint off so you can see better but anyway as pocatello said it will be on the left side of the reciever and you can see the Model 870TB below the wingmaster on the top line.
When you get the serial number then we can date it also or you might check the link above but it only goes from 1921 to 1972 so im sure it will be after 1972 but probably close .
Make sure it says 870 TB on the left side of the receiver. $350 is an excellent price (I just paid $400) IF it is "as new" in the original box. If it has a 30" barrel, so much the better, but at that price if it has a 28" modified or full barrel, it is still a great deal. I can't tell the difference between most field and trap barrels, except for some that have a step rib, which is no big deal. If it has a chrome plated shell lifter (the piece that lifts the shell up to the chamber) it is an early 870 and so much the better. Hope you have found a bargain. Ed
I have a 870TB that is over 45 years old (early 1960's)it was given to me for Christmas by my father (who shot a lot of trap in those days) purchased it brand new. It has a 28" full choke vent rib with the chrome shell lifter and other receiver pieces. I believe that in those years only the trap grade gun had the vent ribs. It has been a great gun and sounds like it has increased in value 4 fold. It has had a lot of shell pass through it over the years and can't remember it ever having a misfire. It shoots where you aim it, it's just that sometimes I don't have it aimed at the right location!!! They DONT MAKE EM LIKE THEY USED TO..