Wow! Just the poesy ring for a linguist!
John has a book put out by the Museum of London called Treasures and Trinkets, subtitled "Jewellery in London from Pre-Roman times to the 1930's."
In a chapter entitled "Symbols of Love", I counted 8 poesy rings dated to the 15th c. The inscriptions are mostly of a similar vein as the one Gwen mentioned- e.g. "nul autre" (no other) "mon cor avez (have my heart- the catalog entry says this is perhaps the commonest medieval posy motto).
Perusing the rest of the chapter, it looks like posy rings continued to be popular through the 17th century, although by that time the mottoes are very different: e.g."Pitye The Poowr" "Joynd in one by God alone" "A Verteous Wife preserveth life". 
The book also has a handy appendix of poesy ring inscriptions, in line-drawings so you can see the mottoes "unrolled" but still get a sense of the letter-forms.
The 15th c. examples have clearly gothic letter forms, while the later ones look, well, later. Either loose, flowy script or chunky block capitals, both looking more like humanist letters.
Gwen- I'll have John bring the book Sunday so you can take a look!
Cheers, ER