Représentent and symbolisent are the best choices here. I wouldn't use the other ones for not being very idiomatic.

By the way "ça parle de lui-même, ce pictogramme, non ?" is dubious.

I would use either:

Ça parle de soi-même...

or

Il parle de lui-même...

Représentent and symbolisent are the best choices here. I wouldn't use the other ones for not being very idiomatic.