"Significar" or "Quiero decir"?

"Significar" or "Quiero decir"?
 

When clarifying translations, I notice that I've never seen a native Spanish speaker use the verb "significar" to say something to the effect of, "I mean," or, "I mean to say;" rather they always use the phrase, "Quiero decir." Is "significar" ever used in this manner? I would virtually never use the phrase "I want to say," to clarify myself in English.

Two different languages. It's 'I mean' in English and 'quiero decir' in Spanish.
There are other ways to say 'I mean', but using the first-person form of 'significar' is not one of them.

In the third person, 'significar' and 'querer decir' can be used interchangeably.
What does this mean?
¿Qué quiere decir esto?
¿Qué significa esto?

O sea, está bien claro, ¿no?
I mean, it's quite clear, isn't it?