Firewall signature / writing ....

I was cleaning up the engine bay on my Barracuda and noticed what looked like a signature or some writing on the firewall after I pressure washed it.

It doesn't look to be scratched in the paint but rather possibly a grease pen or something. It is right above the tunnel and what would be right behind or just above the distributor.

It probably has nothing to do with it but was curious if it was due to it being a factory Formula 'S'.

1965 Barracuda Formula 'S'

The firewall to this point has never been repainted but just wondering if anyone has ever seen this before?

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All kinds of crazy things go on in vehicle assembly plants. The signage that you found could be anything from a ‘Kilroy was here’ notation to a notification that particular part was reviewed and approved by the signer.
Probably not possible to preserve the signage, but I would keep photos of it with the car history as something interesting.