Hi,
The maker is factory of
Alexander Katsch therefore
AK under the crown in the first mark.
In Russian
Александр Качъ
G.P. stands for
ГАЛЬВАНО ПОКРЫТИЕ (electro plated, galvanic silver plate).
Alexander Katch, full name Karl-Wilhelm-Alexander, a citizen of Prussia, was born in 1813. The entrepreneur, founded his business in St. Petersburg, was engaged in both the manufacture and sale of products. The enterprise for the production of cupronickel products has existed since the beginning of the 1840s (in the Directory of 1865, the date of foundation is 1840).
Your plate was bought in his shop in Petersburg.
Regards