It means "ringed". Sometimes in poems, songs, and older English, you might see -ed forms of the verb shortened to -'d. It's not very common, but it is a good thing to be aware of. This is often used in poetry in order to get a word to fit with the rhyme or meter. You might even see poets or songwriters who want a two-syllable word to fit in one syllable. For example, many older hymns might change the word "heaven" to "heav'n" in order for it to fit as one syllable. Again, it's not so common, but it is a good thing to know!

Ringed It is not proper English, but artistic license in a poem