More symbolic than practical, the forked cross has several interpretations
also known as the Y-shaped Cross or Pall Cross
First, let's dismiss a few alternative symbols (shown on the right) that could be confused with the Forked Cross.
In France we see a Y-shaped cross with a single horizontal bar. That is not a Forked Cross.
In China and Japan we see a different Y-shaped cross with a single or double horizontal bar; the currency symbol for Yuan and Yen. That is not a Forked Cross.
And then there's a Y-shaped cross with three prongs; the 3rd image shown on the right (the display of which depends on your browser). That's the symbol of a Trident, a symbol with various religious interpretations. See the page about the Trident for more about that.
This page will focus on the Forked Cross, shown on the left, which has quite unique interpretations.
Looking at the 13th century painting of the Crucifixion, a Forked Cross would probably have been difficult and costly to construct, and it's unlikely that such a cross was made for Jesus' Crucifixion. However, the Bible does say that Jesus was crucified on a tree, and it is from there we get this 'Y' shape.
Many paintings of Jesus on this shape of cross tend to be from the medieval period and show a corpus attached.
Other names are the Thief's Cross or Robber's Cross, since it is believed that criminals in Roman Judea were crucified on a forked cross. However, like many symbols described on this site, there is little irrefutable evidence about their origins. (See the Larron Cross for a further example of a thief's cross, and a suggested reason for the unusual shape.)
With its three members, the Forked Cross reminds us of the Holy Trinity and is often seen on clerical vestments, such as the chasuble (a sort of poncho worn by Lutheran, Anglican and Catholic priests during Mass).
And this leads us to alternative terms - Yoke Cross, Vestment Cross or Pall Cross; pall being an old name for a robe or cloak. However, pall is also a generic name for a cloth that is draped over many different things - a coffin, a corpse, or an altar for example. When a cross is stitched onto a pall, that cross has perhaps more right to be called a Pall Cross.
upsilon or Ypsilon
Here's some useless and not so interesting information: The semaphore signal for the letter 'U' happens to be the shape of 'Y'.
Moving away from Christianity and a few hundred years before Christ, Pythagoras added the letter upsilon to the Greek alphabet, which is '' in uppercase and 'u' in lowercase.
Pythagoreans are said to view the 'Y' as a symbol of one's journey through life. We start life at the bottom of the Ypsilon Cross (Y-shaped Cross) and work our way up through adolescence to the intersecting point. Here, at the crossroads of life, we cannot go forward but must choose whether to branch right, the difficult road following the goddess of Aretê (Virtue) for a blessed life, or branch left on the easy path following the goddess Kakia (Vice) to a life of ruin.
Matt. 7:13-14 tells us to "Enter through the narrow gate. For wide is the gate and broad is the road that leads to destruction, and many enter through it. But small is the gate and narrow the road that leads to life, and only a few find it."
Roman font uppercase 'Y'
Webdings font uppercase 'Y'
'Y' is the initial letter of Yahweh (God's name in Hebrew). Is it coincidence that the Roman font for the letter 'Y' has a broad left arm and a narrow right arm, symbolizing the wide and narrow roads?
Another cross has forks at the end of each arm, called a Moline Cross (Millrine, Millrind, Fourche, Anillée, Nillée, Anchory Cross or Ancrée).
Another name for these multiple-forked crosses is Furca, and that name was also used for an A-frame (inverted Y-frame) used to punish slaves and criminals. Like a yoke, the heavy wooden frame was placed on the victim's shoulders and his hands were tied to the bottom ends. They then had to carry this burden for the duration of their punishment to hinder further crime. Sleeping and eating would be awkward, but many other daily routines would be a severe challenge. When they were released, there'd be much work to catch up on. The device was also employed in the same way as other crosses, for crucifixions.
See also Moline Cross.