This heraldic cross is made from four Latin Crosses arranged at right-angles to each other, with their tops pointing north, south, east and west1. The Cross crosslet, like the Jerusalem Cross, is a symbol for world evangelism of the Gospels, which gives an alternative name: Mission Cross.
Another common interpretation is that it represents the four evangelists: Matthew, Mark, Luke and John (see Evangelists' Cross).
The combination of the four crosses creates a fifth (central) cross, and it is these five crosses that have been adopted by the town of Slupca in Poland. The oldest known appearance of this crest is on a seal dated 1404, and the reason for chosing the design is lost in history. The town's website www.miasto.slupca.pl/ speculates that the five crosses symbolize the five churches that existed in the city at that time: The churches of St. Lawrence, St. Mary, St. Leonard & Chapels, St. Cross and St. Spirit.
The Cross Crosslet is sometimes confused with the St. Julian's Cross or Jerusalem Cross.
Where only three Latin Crosses are used, the symbol represents the Trinity. Often the cross is fitched, with the lower crossed-arm is replaced by a sword blade, as in the Cross of St. James.
Other names for the Cross Crosslet include Crossed Cross (Fr: Croisé), Recoursy Cross (Fr: Raccourci) and Recrossed Cross (Fr: Recroisetté). An artistic variation of the Cross Crosslet is the Bottony Cross.
An example of a fitched Cross Crosslet can be seen in the photo of a Donegal Cross on the right (click the photo to enlarge), with its detail shown adjacent.
An example of a Cross Crosslet Crossed can be seen in the centre of the coat of arms used by the Patriarch of the Romanian Orthodox Church.
Above the cross is a descending dove and flanked by two aquilas (eagles), which also feature in the country's coat of arms. These three elements are enclosed in a shield.
Above this shield is a crown and flanked by angels.
The above links detail the meaning associated with each variation of the crosslet. For the meaning of the crosslet itself, see The Four Corners of the Cross by Rev. David Linde.