Generally in terms of a noun, you'd be looking at a **significante** (which often is paired with *significado*, or the *signified*)

It sounds a bit odd in the structure of the sentence you have, though.  I would rewrite it as such:

> A y B son los *significantes* de tal concepto.

If you want to retain the structure (and you're not doing a signifier/signified-type relationship), you could say something like

> A y B *<sup>significan</sup>/<sub>representan</sub>* tal concepto.  
A y B *<sup>simbolizan</sup>/<sub>designan</sub>* tal concepto.  
A y B *<sup>encarnan</sup>/<sub>personifican</sub>* tal concepto. <sub>(more commonly when A/B are animate)</sub>  
A y B *son* un símbolo para tal concepto.