Mysterious Square Seamaster ... Help, Please!

I would love to know more about this Automatic Seamaster. I cannot find a reference number on it anywhere, and to be honest, it looks like it's been well-used, but it's still working. I inherited it from a deceased relative, so I have no documentation, etc.

I'm a woman with slim wrists, and so it's not quite to my taste (too chunky for me!) so I'm thinking about what to do with it.

I'd be grateful for any information! I can't find out much from the Omega website ...

Thank you!