KEEP OUT. Four kanji that look like a proverb and are a fence sign.

What a Japanese person actually thinks
Instantly, unmistakably a sign. The four-character shape makes it look like a yojijukugo, which is precisely why it ends up in flash books — and precisely why it's funny.

Meaning

Literally: entering + prohibited
Actually: No entry. On construction hoardings, closed trails, restricted areas.

Scores

Naturalness●●●●●

Correct.

Coolness●●●●●

If the joke is intentional — 'do not approach me' — it's actually quite good. If it isn't, it's a fence.

Watch out

highFour kanji in a row is the visual signature of a classical idiom. It's also the visual signature of official signage. You cannot tell them apart by looking.

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孤高 kokō
aloof and alone by choice; standing apart on principle

If 'keep your distance' was the sentiment, this is the dignified version — solitude as integrity rather than as a barrier.

On skin

立入禁止

Orientation: vertical

N/A unless the joke is the point.