Question What are these yellow marks on the back of my Samsung phone?

[janseana]

I discovered my old Samsung a7 2017 (A720F/DS) in my drawer and found several yellow smudges or stains on the back cover (which is made of glass). Nearly a year has passed since the phone was last used (with no battery left). Who has any idea what this is? Should I throw this away?

https://freeimage.host/i/HKR4XOx

 

[COLGeek]

Looks like residue from a previously installed protective case/cover.