Cross Crosslet
Another common interpretation is that it represents the four evangelists: Matthew, Mark, Luke and John (see Evangelists' Cross).
Slupca town crest
The combination of the four crosses creates a fifth (central) cross, and it's 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 choosing the design is lost in history. The town's website https://www.miasto.slupca.pl/pl/1/280/herb_i_flaga_miasta 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.
Gravestone in Rudna Glava, Serbia. Photo by Nenad Bačilović
A further example can be seen further south in Serbia on the late-19th century gravestone shown on the right (Click image to enlarge). This was photographed in a Rudna Glava village in eastern Serbia and may have Vlach influence.
As far as we know there are no detailed cemetery records to indicate whether the deceased had a senior civic or military role, so we don't know if this crosslet is heraldic, religious, or just the whim of the mason or deceased's relatives. If you have information about this, please let us know.
The St. Julian's Cross, one of several Missionary Crosses, is another example of a Cross Crosslet.
The Jerusalem Cross, however, is not a Cross Crosslet, though it's often confused to be.
Crosses on the arms only are not uncommon.
Here we see a Gothic-style example between the towers of the 14th century Church of Our Lady before Týn (Týnský chrám) in Prague. (Click photos to enlarge.)
No, it's neither the logo of International Harvester, nor the abbreviation for Hawaii. If it's an acronym of anything, then it would be the Greek iota (I) and eta H, being the first two letters of the Greek spelling of "Jesus".
Fitched cross
Where only three Latin Crosses are used, the symbol represents the Trinity. Often such crosses are fitched, where the stem is shaped as a sword blade, similar to the Cross of St. James.
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).
Cross Crosslet Crossed
Romanian Orthodox
(Click image to enlarge)
We see a Cross Crosslet Crossed in the centre of the coat of arms used by the Patriarch of the Romanian Orthodox Church.
On that emblem, 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 the shield is a crown and flanked by angels.
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.
The above hyperlinks explain 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.
See also Cardinal Cross