My brother bought a 2003 Chevy Impala and on the inside of the trunk there is a leather strap that is installed on the trunk lid. This strap is for pulling the trunk closed, making it so you don't have to touch the outside of the trunk to close it, just pull on this strap.
We looked at my car and it has the same square notches in the trunk lid for the same type of strap.
Went to a auto salvage yard today and found the same strap in a 2003 Impala, got it for $5.00, and now I can close my trunk without having to touch the outside at all, just tug the strap and let go within about 1-2ft from the closed position, get hand out of way and it glides down and shuts. Actually takes less force this way it seems, just different arm movement, and is a nice way to keep the trunk lid clean. I'm not sure if most GPs come with this strap or not, but mine didn't so I just bought a strap from an Impala.
GM Parts Direct has the part listed for $7.48. MSRP being about $12.19. Part #12 in the diagram.