I’ve never seen that before. That’s one of those situations where you wonder if the adverb or the adjective is the best to use, are we describing the act of knocking or the actual knock itself, personally I am used to the latter. I do find myself thinking twice about these examples though.

Hypercorrection: linguistic insecurity inspired by over preoccupation with grammatical “rules” proclaimed by fiat…

Damn that autocorrect! Overpreoccupation is what I typed but it thought it should be split into two words.

It reminds me of those situations where some people say things like “between you and I” because the prescriptivists have drilled it into them that it’s “incorrect” to use ‘me’ in the subjective sense, so they hypercorrect and hardly (;p) use ‘me’ at all…I think it’s sad…

I think if they meant “little” the note should say “Please hardly knock”.
When I first read the phrase, I directly understood they meant “knock hard on the door”. Probably the owner is HOH!

My guess is a non-native speaker who wants people to knock in a forceful manner.

The only way to know for sure is to knock loudly and see if they mnd…..

Yup, like “They hardly said a word” which, of course, means that they BARELY said a word, not that they said said word with great emphasis :)

Cheers,
Andrew

And of course, That they “barely” said a word implies nothing about their state of dress. It all boils down, in my opinion, to overzealous application of the rule that if something is an adjective, you have to add -ly to make an adverb. Like the misguided criticism of Apple’s ad slogan “Think different”: self appointed grammar police said it should be “Think differently”, not understanding that the adjective was being used as a (stranded) predicate.

Yeah, it definitely looks like a non-native usage grammatical error maybe influenced mistakenly by ‘knock loudly’ and it does pop up a few times if you google the phrase as erroneous adjective and adverb forms of ‘hard’. That’s just one of the English language’s quirks where the same word could be either a noun, adjective, adverb &c. depending upon context solely.

That reminds me of some silly signs and notices I’ve seen around Liverpool city centre. This isn’t a grammatical error but I once saw the tiniest of one-man ice cream kiosk with a sign saying ‘vacancy – apply within’ which made me chuckle seeing as it wasn’t even large enough for two adults to fit in comfortably. But back to grammatical errors, the dreaded greengrocer’s apostrophe is still pretty rife even on shop bought signs ie. ‘Happy birthday lot’s of love …’ (sic) and I’ve sadly witnessed it on gravestone inscriptions ‘missing you load’s’ (sic)

On similar tracks I’m always surprised by the French for “to work hard” which is “travailler dur” – not the adverb you’d expect.

Folowing on from above I see in my dictionary that “knock hard” in French is also “frapper dur”. I wonder why the coincidence that the French form is an adjective used adverbally (and a rather rare phenomenon I think in French) just as in English.
Can any bright sparks out there shed any light?

I’m reminded of that playground joke:

– Why did the chicken cross the road softly?
– Because it was very old and couldn’t walk hardly.

Does that work only in British English?

I’m in Nepal right now and I’ve noticed people use ‘hardly’ in this way quite a bit when speaking English: “Please try hardly on this test,” “Push hardly on the door,” etc. You can say that this is an English language learning error, or you could say that this is an element of a developing variety of Nepali-English I guess.