I'm not Irish but Claddagh rings can show a person's availability, as it were, according to how these are worn:

On the right hand with the heart worn outwards, it indicates that the wearer is single and available for courtship. Worn on the ring finger of the left hand with the heart outwards it shows that the heart is occupied, but not yet married. Worn on the left ring finger with the heart facing outward symbolizes an engagement. Worn on the left ring finger with the heart facing inwards the Claddagh Ring declares that the wearer is married.

AMDGJMJ, I'm not saying to get Claddagh rings for all the attendees. But there could be some sort of color-coded system of wristbands or nametags, maybe optional to wear as each person wishes. 

As for me, I'm echoing Seraphina and Fifteen Decades Daily!

Maybe we could add a sticker "open to courtship" on the name tags or would that be weird?

A couple points --

1. Some people (especially ladies) can be very shy on this topic. That's why you need to make sure it doesn't get left out. BUT
2. I think it would be best to go for SUBTLE, again, because a good feminine woman will be bashful about advertising herself. So I think "open to courtship!" would be too forward for some (many?). I think something more like a color code, the border around the nametag, or something.
3. I should also add -- this color code is for the benefit of those seeking spouses AND those NOT seeking spouses. Both types will be interested in some kind of system, subtle but effective, to let everyone know who is available/interested in romantic attention -- and who is not.
4. There's also the phenomenon that many people aren't open to love/marriage until they meet the right person -- then they totally change their mind. So you don't want to force them to commit to a person they are unaware of, who doesn't exist to them yet. It's kind of like going against nature. Just let them think they want to stay single. So you have to be careful how you word it -- I mean, how you ask them "are you open to courtship?". Now that might actually be a good way (the best way?) to ask the question; I'm not shooting it down. I'm just throwing this point about human nature out there.

There are a ton of different ways to accomplish this, I'm sure.

This is why it's sad that old-timey courtship signals fell out of favor.  Use of fans, flowers, even hats for a lady to let others know they could approach or not.  Even demure maidens could flirt!

For any men from Michigan or Northern Ohio interested in the event:

There is another man from the area looking for someone to travel with and share traveling expenses.