Jehovah's Witnesses believe that Christ was crucified on an upright stake or pole rather than a cross. You're probably thinking, either way, what's the big deal? I agree that this is not a huge issue, but it shows yet one more thing the Jehovah's Witness religion is not accurate on.
Here is a snippet taken directly from www.watchtower.org, the Jehovah's Witness' official Web site which explains their view about the cross in a nutshell:
"Jesus did not die on a cross. He died on a pole, or a stake. The Greek word translated "cross" in many Bibles meant just one piece of timber. The symbol of the cross comes from ancient false religions. The cross was not used or worshiped by the early Christians. Therefore, do you think it would be right to use a cross in worship?"
Deuteronomy 7:26; 1 Corinthians 10:14.
This Watchtower quote touches on two topics relating to the cross, which I will discuss further down below:
The JW's believe it was a straight pole, but the Bible speaks of being hung on a tree ( Galatians 3:13 and Acts 5:30 ), and all 4 gospels mention that a cross was carried to the crucifixion site ( Matthew 27:32, Mark 15:21, Luke 23:26, and John 19:17 ). Well which is it? To answer this, we must first take a look at the crosses used for crucifixions in those days.

Here you see a picture of the 3 most common types of crosses used by Roman soldiers during the 1st century A.D. Each cross had a sign on the top that displayed the victim's offense.
Most crosses we see today take after the middle cross above. This cross was known as a "low tau" because the shape resembled a Greek lowercase "t". The cross to the left was called a "high tau" because it resembled a Greek uppercase "T". The cross to the right was commonly referred to as a "tree" because of the resemblance to a tree (Just a little joke). This tree, either dead or alive, was left in the ground rather than digging it up, having to transport it, and then re-dig it back into the ground again at the crucifixion site.
For a more detailed discussion about how the cross used to crucify Jesus was not a straight pole as the Jehovah's Witnesses believe, read this article written by Ron Rhodes.
The next point the Watchtower makes is that the symbol of the cross comes from ancient false religions and that it was not worshipped by the early Christians, then goes on to ask if it should be used in worship today.
First of all, I would like to make it clear that there is an enormous difference between using (or having) a cross in worship and actually worshiping the cross itself. I feel that the Jehovah's Witnesses are not making a distinction between these two and therefore think that being in possession of a cross is just as bad as worshiping the cross, which is just not so. If you worshipped a cross you would be in violation of God's commandment against idolatry, which brings us to examining the two verses the Watchtower cited to back up their reasoning against the cross:
The first verse they reference is Deuteronomy 7:26 which reads,
"Neither shalt thou bring an abomination into thine house, lest thou be a cursed thing like it: but thou shalt utterly detest it, and thou shalt utterly abhor it; for it is a cursed thing."
This verse speaks directly against idolatry. God was leading his people to a destination where the current nations living there practiced idolatry, specifically worshipping carved images. God was commanding his people against engaging in this idolatry and letting them know they will be cursed if they bring the abominations (idols) into their houses. This verse does not apply to having a cross hanging on your wall unless you are worshipping the cross instead of God.
The second and last verse the Watchtower references is 1 Corinthians 10:14 and reads along the same lines as the first,
"Wherefore, my dearly beloved, flee from idolatry."
Again, we have another verse letting us know that idolatry is bad and wrong and we should flee from it. I agree, idolatry is wrong and should not be practiced, but crosses and idolatry have nothing in common unless the cross is being worshipped.
The only two verses the Jehovah's Witnesses could provide against having a cross both failed to show why a cross itself is bad. Since there are no other verses given, I have to assume that the Watchtower is unable to come up with one acceptable reason to avoid the symbol of a cross.
I highly recommend reading this article taken from wcg.org that discusses both the physical structure of the cross and its pagan aspects.
It appears that the Watchtower organization and the Jehovah's Witnesses that follow it have missed the point as to why a cross would be used. A cross seen hanging on a wall, on a key chain, or in a picture is nothing more than a visual reminder of the awesome miracle that took place on it. We save our worship for the risen Christ and Him alone do we praise.