neat looking old pin I would think it has something to do with the letters in the center C E or E C .don't think it has anything to do with Juneteenth as it would be the 19th not 18-20 could be wrong.
The EC sort a looks like the Continental Emsco logo. They've been around a long time.
<img src="http://www.treasurenet.com/forums/attachment.php?attachmentid=822460"/>
I don't necessarily think the 21 stands for 1921 because June 19, 1921 was on a Sunday, and it was Father's Day. It's a possibility the 19-21 meant the conference was held on the 19th, 20th, and 21st.
Just a thought,
Breezie