Should protestants not make the sign of the Cross? I'm not a Catholic, but I've been aware since I was little that Catholics will "Cross" themselves. Early on I felt like I shouldn't copy it as it always had been portrayed in tv/film as something ritualistic or superstitious. But now that I understand some of the Catholic's reasoning, I'm wondering if there is any doctrine in protestantism that addresses why you shouldn't do it, or is it simply because we don't want to imitate Catholicism? 

Catholic brethren please feel free to talk about the reasons why it should be done, in the comments.
I don't think there's any harm in making the sign of the cross.  I don't think we could equate it with the type of superstition that equates to idolatry or occultism.  (I'm sorry if that sounds offensive to anyone who practices it.  Please read on, and you'll see I don't mean to offend.)

It's definitely meant as a Christian gesture for the Catholics and the other denominations that did or still do practice it.

I think that if you're a protestant that is not in a denomination that practices it, you should not practice it.  Not because it's wrong, or for Scriptural reasons but because there's really no good motive to do so and because it just plain shows common decency to respect the traditions of others, so long as they are not anti-Christian, or anti-God.  

To do it flippantly would seem to dishonor it and could prove offensive to those who hold it as important.  As a Baptist, I imagine I'd get annoyed if a bunch of Catholics went down to the beach and held dunking-style baptisms just to do it.  To me, baptism is very symbolic, and an important rite. Not that it saves you or anything, but it's not something to be made fun of.  For those that make the sign of the cross, I'd imagine it's the same.

Since there is no scriptural prohibition against it, and it's important to some, I'd say that we should just keep our silence, and show respect for their beliefs and practices, as we'd hope they'd have respect for ours.