Today, we have Catholic and Orthodox churches (and a few others) using the crucifix, whereas most Protestant denominations use an empty cross in their symbolism. Did this difference in symbolism arise around the time Martin Luther "created" the Protestant church, or did it happen at a different time? Also, what caused the change of symbol?
In history there have always been reasons to show a crucifix without a corpus.1 Especially in the first four centuries of Christianity it was – because of theological reservations – not possible to illustrate the suffering servant figure of Jesus Christ: They thought that it was not beneficial for the majesty of Christ's divinity.2
Another trail leads us to Calvinism: Also there led a sovereign, bordering to the abstract image of God to a sober view of the cross without a corpus.3
1: Burkard Porzelt, Empirische Religionspädagogik, 175
As an Eastern rite Catholic, we have our priest holding crucifix to bless us during each divine liturgy. Because Roman rite Catholic, Eastern rite Catholic, Eastern Orthodox, Oriental Orthodox (non-Chalcedonian), and Assyrian Church (non-Ephesian) use crucifix we can safely estimate that this practice date from the early church before schism happened for the first time at 431 in Ephesus.
The depiction of Christ on the cross exist along with iconography in the early church. Assyrian Church to this day rarely use iconography due to heavy persecution during the Sassanids. Prior to that Assyrians were known to practice iconography openly. It is highly debated among Christians when iconography was introduced. Some argue iconography at Roman catacombs merely depicting an early corruption of Paganism into Christianity while others argue that it's a direct evidence of an early apostolic practice. Due to its argumentative nature of this debate I try to be neutral and address both viewpoint as neutral as possible. So it's difficult to argue when the empty crucifix symbol occur. Due to the existing crucifix symbol prior to Reformation it can be safely argue that such reform might took place during iconoclastic reformation in the late 16th century Europe.