Hi,
It's not an anchor, the mark on your item was taken from the burgh arms of Glasgow. An oak tree surmounted by a salmon with a ring in it's mouth and a bell.
Here's a clearer image of what your mark would have looked like:

Remember that at this time, Glasgow had no assay office. The town mark would have struck by the silversmith himself, with his own punch, so there would have been considerable variation with this mark, not only with that of other silversmiths, but with any replacement that was required over the years.
Trev.