English equivalent to the Portuguese expression “entendedores entenderão”, “those who understand understand”?

In Portuguese, “entendedores entenderão”, which literally can be translated to “those who understand understand”, is often used on the internet.

Someone might write this when (s)he posts something that only people with knowledge on the subject would be able to comprehend. For example, when posting a joke about mathematics.

Is there an idiomatic expression that means the same thing in English? I tried googling the phrase “whoever gets it”, hoping it would lead to some expression, but I did not find anything.

The common expression in English is "If you know, you know."

Urbandictionary has a good definition:

The defining phrase of an inside joke/access to information only a select few know about

Since those who understand will understand without much explanation ...

A word to the wise is sufficient.

The saying introduces a statement as advice: A word to the wise—never sign a contract without reading it first.

I have heard:

(Only) Those in the know will understand.

Collins explains that

If you are in the know about something, especially something that is not known about or understood by many people, you have information about it.