Hi, Definitively Hanau.The only swan mark I recall was used by Johann S Kurz & Co but their swan is usually with initials.On the other hand, they were in business for 100 years, probably the mark had significant variations. Regards
I have just spotted this swan mark on a tea caddy by Neresheimer. It is on eBay hence I cannot provide the photo but there is no mistake. The identical swan mark is stamped beside the s517 and s520 Neresheimer marks. It also has Chester import mark and date letter for 1903.