Insurance does have a number but you cannot look it up...only the post office can on their service network. If it is $200 or less, no signature is required. If it is $201 or more, then a signature is required. I cannot believe the sender does not know about Delivery Confirmation or Signature Confirmation. The clerk at the post office asks if you want that service all the time. Fingers crossed. There are no green insured stickers. Certified is kelly green, Del. Con. is bright green, Sig. Con. is bright pink, insured under 200 is black, and over 200 is blue if they use USPS forms. If they do it through PayPal or Shipping Assistant then there are no colors. I have been retired for 2 yrs so I am going from memory.