They might be obvious ones in the context of this one person. But they are trivially not obvious next to someone who writes one like "|" and then seven is just "|" with any sort of hat. Your slant heuristic immediately fails.
It's "obvious" because 7 is always slanted here. But I know it's not the case in North America and I have a good experience on how numbers can be misinterpreted, as I said.
I was just saying it was obvious to me and it even takes effort to see how they could be misinterpreted. But I know they can be.
