It is used on vehicles equipped with DISTRONIC (radar adaptive cruise control). The radar sensor sits behind the smooth emblem, so the star is made of radar-transparent material rather.
Common Mercedes-Benz models that use this type of grille star include:
C-Class (W205, W206)
E-Class (W213)
S-Class (W222, W223)
CLA (C117, C118)
CLS (C257)
GLA (X156, H247)
GLB (X247)
GLC (X253, X254)
GLE (W167)
GLS (X167)
A-Class (W177)