I have noticed that more and more event cache pages are listing sponsors or contributors, both private and commercial. This practice must be done with caution, so as to not violate Groundspeak / Geocaching.com's policy on commercialism. For your future reference, here is the official policy on the listing of event sponsors on event cache pages. Please follow this policy or your event page may be archived.

Generally, sponsors may be listed by name on event pages but no links, logos or URLs may be included. This is done to avoid having the event pages become billboards for advertisers.

So, the note could say, 'Thanks to Joe's Market for sponsorship of this event', but not 'thanks to Joe's market.com...' Again, we don't want event pages to become listings and links of sponsors and if we allow one to do it, everyone will want to sponsor events so that they can get advertising on the site event pages.

Another option would be including something like a link to a specific non-commercial off-geocaching.com event landing page. On that page, as long as the purposes is really to provide event info (as opposed to a venue for advertising) links, logos and URLs could be included.