I have seen a couple of different implementations of admonitions in Markdown.
These are:
>
Using blockquotes (MS & Github).
Like @pboling said, I don’t think this is ideal, since an admonition is not a quote.:::
Using three colons to start and end a block (Docusaurus & Quarto).
This defines a clear boundary of and admonition block.!!!
Using three exclamation marks (MKDocs).
This implies importance and doesn’t really work well for a note or a tip admonition.
My preference would be to go for option 2.
I think using emoji is a good idea for keeping it easy to read in all languages:
::: ℹ️
This is some info
:::
::: 💡
This is a tip
:::
::: ⚠️
This is a warning
:::
::: 🔥
This is danger
:::
So, basically, what @bb010g already proposed