It means that it is a Model 1890 (90) receiver. When Winchester introduced the Model 1906, they used the exact same receiver and action as the Model 1890, with exeption of the cartridge carrier. To readily differentiate between the two, Winchester stamped an "A" on the Model 1890 receiver and a "B" on the Model 1906 receiver. Bert H.
On the receiver
Receiver
This firearm has benn overhauled at the Winchester factory and a different receiver installed. James Friend
Receiver
Receiver.
Check the receiver.
Receiver.
Your Marlin model 1894S was made in the year 1988 with the serial number that you have supplied.
Bottom of receiver
Check the receiver.
Bottom of the receiver