Let's not forget Biblical support:
John 20:25, where Thomas says, " Except I shall see in his hands the print of the NAILS......I will not bellieve." (as apposed to a single nail driven through both hands.) Of lesser significance, but still of interest is that Matthew 27:37 says that the sign hung on the cruxifix was placed above His HEAD (as apposed to being hung above his hands.)
Bottom line: It is not significant one way or the other. All that matters is the fact that He did sacrifice his life, not upon what device. In the spirit of Romans 14 - 15:1-7 we should not judge one another's belief on the matter, AND we should exercise caution not to cause another to turn away from Christ by insisting on our own point of view.
Therefore, if I expected to see JWs, I would not wear a cross, knowing that they veiw it only as a pagan symbol. When discussing it, I like to emphasize that we really do not know for sure, but for these reasons, I cannot say that it was not a cross. I point out that those that do revere the cross do so as a rememberance of Christ's sacrfice, and therefore are "doing it into the Lord."
Since most JWs insist that stauros means a single pole, I point out that if He were carrying the crossbeam, which would be attached to the upright pole at the torture sight, it would in fact be a single pole that he carried. And as a point of reason, would it be possible for a man to carry a pole that was large and strong enough for him to be impailed upon it? or is it more reasonable to think that the crossbeam, which would be much smaller in comparision, would be the more likely piece of wood carried by Jesus.
My only goal in this kind of discussion is to allow the JW to see that there is a possibility that Christ was tortured on a cross, and that revering a cross does not chaulk one up as a "false Christian."
Romans 14: 4-6,14,22-23 says 'Why do you judge another man's servant. It is up to his master whether the servant's actions are pleasing or not. In fact, when we stand before God, He is able to view us all as pleasing. When it come to these matters of concsience, let each person be sure in his own mind what he thinks is best. That way every person that engages in a practice, does it for the glory of God with thankfulness; and everyone that refrains from a practice, does not do it to the glory of God, also with thankfulness. I am absolutely convinced by Jesus Himself that there is NOTHING unclean. But, if a person's conscience views it as unclean, then for him it is unclean. You would not be showing Christian kindness to him if you insisted on having it your way in front of him. You could be responsible for turning him away from the Lord. Be happy to exercise your practice before God. Avoid pressuring others to do the same, for them it may be a sin.'