Sugar bowl Hallmark help please

I am stumped! These marks are on the bottom of a beautiful heavy handmade covered sugar bowl. Any help is greatly appreciated!!!

I’m going to guess that this is silver planted, and that the number is a 150, which would mean 150 grams of silver either for that piece, or for the set if it was part of a set. 150 seems like a lot for one piece. But, really, I’m just guessing, I’m not familiar with those marks myself. The EM is a maker’s mark, but I have no idea for which country so that you could have a direction to search.