Unbranded Movement in 1930s(?) Oyster

[aesmith]

Hi,

This watch belonged to a family member, I don't unfortunately have any detailed history. What I find a bit strange is that the word "Rolex" doesn't appear anywhere except on the dial. Not on the back, or the inside of the back or on the movement. The back just has a couple of numbers 121018 and 3121. Inside back is marked Oyster Watch Co, and the dial says "Rolex" and "Oyster" on two lines. The crown is marked ..



I was surprised not to see Rolex branding other than on the dial, other pictures of similar age watches show the name appearing on the movement and on the back.

Any thoughts or comments?

Thanks, Tony S