Observant pedestrians in Portland have likely noticed these manhole covers that were made locally by Etheridge Foundry.
Below is a recent photo of the Etheridge Foundry headquarters, located on Ocean Avenue almost in Falmouth. I'm not sure how much business they do these days. I wasn't able to find any info about them on the internet other than their blurb on Manta.com: Etheridge Foundry & Machine Co in Portland, ME is a private company categorized under Manhole Covers Manufacturers. Our records show it was established in 1927 and incorporated in Maine