Trent,
I'm sorry but that sounds like a total invention-fabrication. A just-so story. A case of "Well, this is the best way I conceive it happening, and therefore that's probably how it went down." Could someone have used simple drawings in the dirt to accentuate what they were saying? If we can do it today, I guess they could have done it then; but proposing a formula? Apostolic-approved stick diagram? It's just wishful thinking.
How did the early church evangelize? The book of Acts contains over a dozen instances of evangelism in various forms, from expository sermons, to earnest exhortation, to confrontation of various kinds. The main thing is that were talking "news," you know--like what you read in print, with headlines. Good news, prefaced of course by a restatement of the bad news. Men simply repeating God's Word is what conveys the vital truth. The Spirit uses words, not images.
The NT doesn't give us any symbols, other than bread and wine. Did people do much drawing-in-the-dirt, or graffiti, when they were relaying information? Any information? Were pictures the way news from Alexandria was explained to the man on the street in Rome? I think the whole idea of illustrations presupposes a certain attitude toward conveying knowledge person to person. But that attitude is not universal.
I think the notion of relying on symbols is pretty reductionist. The authoritative symbols in the NT (bread and wine) demand thinking and reflection, they presuppose the rational human mind that God created. The NT is chock full of various word-pictures, but those weren't necessarily conceived in order to provide subjects for artists.
Symbols eventually get carved in stone, embedded in mosaics, written about, etc. The little lines you mentioned are nowhere to be found; they were not preserved because they never existed. (Wait and see, someone will now produce a relic...)
