Why do some summons have forehead protector while most of others don't? These are all summons with forehead protector that I can find, it's quite rare among the summons. For example, Sannin's summons, Inuzuka Clan's Ninkens and the Ninnekos don't have forehead protectors.

Are the headbands are overall just for decoration purpose for the summons? 

Weren't forehead protectors are worn by most Shinobi since the summons are technically mini ninjas?

Kakashi's and Guy's summons:


Konohamaru's summons:


Hiruzen's (Third hokage) summons:
Forehead Protector in Naruto shows the symbol of Ninja's hidden village and his loyalty towards it.

Similar can be assumed with Summoned animals, Summoned Animals with Summoned animals with  forehead protector seems to be loyal to one village only.

Even naruto.wikia.com speculated the same :


  Summons may also wear a forehead protector, suggesting a loyalty to
  only one village.