The Cruces are symbols very used in the flags. They are used from the time of The Crusades, and is a common element in Heraldry, there are hundreds of models, these are most common:

Symmetric cross / St George's Cross.

Scandinavian cross.

Saltire / St. Andrew's cross

Equilateral (Greek) cross.

Latin cross.

Patriarchal cross / Cross of Lorraine.

Maltese cross.

Jerusalem cross.