A Funny Thing About The Ten Commandments

This morning a friend of mine mentioned that there's usually a senseless (but traditional) mistake in our representations of the 10 Commandments. He was referring to political hacks who put the traditional outline of the stone tablets on campaign posters as a shorthand for "I'm for traditional values." The mistake is prominent on this poster. Do you see it?

If you look closely, you'll see that the mistake is repeated below on an infamous statue outside of a courthouse. Don't get hung up on the extra verbiage they left out from the biblical account in Exodus 20:2-17. Don't do a textual analysis comparing this version to the one in Deuteronomy 5:6-21 either. Both texts are similar but not identical (which you would expect from documents claiming to be the inerrant word of God.) Plus, almost all of our 10 Commandments artwork omits the biblical threats against those who break the commandments.
(This dispute apparently was a plot point on an episode of The West Wing TV series. You can read a compact summary of the discrepancies, and resolution, here.) But that's not the mistake that my friend told me about.
A group called Team Sandtastic made the same mistake in a sand sculpture. Look for an anachronism.
You'd think God would give us some prohibitions against slavery, or define when life begins during pregnancy. A commandment against racism would've been nice, but that would've slowed down the ongoing Jewish campaign against the Canaanites. (Something about being God's chosen people clashes with prohibitions against racism, doesn't it?)
But I digress. The first three commandments on the poster below seem petty. The remainder seem like unnecessary reminders. But the arbitrary nature of the commandments isn't what my friend told me about.
The mistake is on the poster below. Moses is holding it.
This next picture looks like someone went to a lot of trouble to cast the tablets out of cinder blocks. The text isn't legible, but the error is there for everyone to see. (I believe the mistake is usually made in an effort to give the commandments an air of ancient authority.)

If you still haven't found the mistake, let's oversimplify the pictures. This picture came from The Confederate States Of America Website.... (speaking of organizations that try to give themselves an air of ancient authority.)

Give up?

Don't. Here's the same thing on the the door panels to the Supreme Court....(some skeptics claim that this door panel depicts the Bill of Rights.)

The answer is blaring at you.

Ok, here goes. If the 10 Commandments came down from Mount Sinai around 2,300 BCE, they were chipped into stone about 2,000 years before the birth of the Roman empire. That would be 2,000 years before the advent of Roman numerals. So there is abolutely no reason to list the things with Roman numerals.

We traditionally use Roman numerals on grandfather clocks, in our scholarly outlines, and for some reason, copyrights. But all of these came after the Roman empire. We still use the numbers I-XII on sundials, since the Romans had sundials.

But why are they always on the Ten Commandments?

Well, can you imagine this on a statute outside an Alabama courthouse? Lilah Tov !