Why do only some pets have the PPS watermark?

[KariaTheCat]

I mean
These are all PPS chicks, why do only some of them have the PPS watermark?

[OnAStorytellersNight]

The ones without the watermark are full grown birds, the others are ducklings.

[bin]

Sometimes when it comes to event pets, cs doesn't put the pps symbol EVEN if it's pps. It really doesn't mean anything but it's just some lines are small and the pps logo is large.
..Examples-
<- no pps sign, 100% pps though.

<- pps symbol.

[Lennie]

Just to tack on, Seasonal actually answered this in the Easter Event - Casual Chat ^^

If you click the birds they still say pps underneath though
That’s why I’m wondering why only the ducks got it as part of the image

They were made by two different artists. One artist used the PPS tag and one did not. ^^