A horseshoe is like a luck charm
"The horseshoe has always been associated with good luck in Irish folklore. Brides traditionally carry a horseshoe with them on their wedding day for good luck. After they set up their home together, the horseshoe is hung over their front door to continue to ward off evil and despair.
These days, horseshoes sold as Irish wedding gifts are usually made of porcelain and will often have lovely Irish or Celtic designs. Just remember, if you give the couple a horseshoe, give it to them with the "U" facing up - this way it stops the luck from draining out! "
I got given one on my wedding day and didnt have a clue what it was for, but still carried it round not having a clue about the upside down thing! lol x