Bonjour je suis en 4eme , pouvez vous m'aider pour mon slogan,svp merci.

Hello!

Here are a few I came up with but I don't know if it's good.

Not knowing the sender, can be a danger.  (the danger of messaging unknown people online)

Think before you post for it can be unsafe. ( the contents of your post can be harmful...

Don't be a fool to try to be cool. ( foolish people do foolish things online for fame.)

I hope that this has helped/inspired you ♥