Cornellia suggested the Tara brooch and I second that! *S* It's about as widely recognized as "Celtic" as the crosses. Although Irish, similar penannular brooches have been found in burial sites throughout the Celtic realms (unlike the Celtic crosses, which are found mainly in the UK and Ireland). If everyone agrees on the brooch as Celtia's symbol, here's a transparent gif I made of the Tara brooch for the Meath web ring tour that you are most welcome to use as your model for the plaque: If you need a larger image to work from, you can use the one in the Celtia Family Plaques thread header.