My recomendation would be to imply no affiliation with ETS, just in case you FU and simply because it ain't true.

I would [and will, now that you mention it], put some date on the reverse side of my cards.

Perhaps with a benign something such as: "Member of . . . " along with other professional or other affiliations? Doug's graphic designer might be able to post a 'bug' you could down load.