Small green stacked German vase with unknown marking

I found this small olive green vase at a consignment shop. It has a very geometric design with alternative sections of thick / thin stacks. The bottom is marked "made in Germany" "233 / 73" and has a mark that I can't identify. It almost looks like an "st" or a foreign letter. Would love to hear any ideas! This is my first post.

photo required , but sounds like it may be steuler .

Sorry, having a technical problem...photos coming shortly!

Got it...thanks!!!

ok , not sure it's marked 13 at the end not 73 , possibly soendgen keramik , but as I say not sure , I think Volker will know when he sees it .

Big Ed solved this before, some months ago,  and I can just confirm that the sign has to be read SK (conjoined) which stands for Söndgen Keramik, it´s later than i thought  at first look.

Thanks! Much appreciated :)