h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

I posted this on the forum of the approved Guide Entry for the said Christian Fish http://www.h2g2.com/A273610 . I'd appreciate any comments or confirmation anyone out there can offer. Thanx.

In the Roman days, you would most likely be killed for practicing the Christian faith. So, in order to have their sermons and churches and stuff, they went into the catacombs (combination sewer, gutter, and morgue). Because of this association with the dead bodies therein, Christianity was considered a *very* sick little cult, adding to the already shunned people's discomfort.

Now, what does this have to do with the fish?

-----Ok, this is a little aside, but it's necessary. What I'm about to say is unconfirmed by any well-known source. If you know anything about this, feel free to say so. I would love to hear it.-----

Well, to distinguish the practicing christians hiding in the sewers from the drabble of theives and murderers hiding in the sewers, the christian would, very nonchalantly, draw a half-circle in the dirt. Then, the other man, if he were not a christian, would merely think it odd. But if he were a christian, he would respond with another half-circle in the dirt, completing the simple two-line fish. Thus did the christian catacomb refugees recognize others without getting caught (and subsequently executed).