Code SL
An SL postmark code indicates a Straight Line Marking.
The following postmark is classified as Code SL3bs (46×2)
Code SLK
“SLK” is a Straight Line Killer, struck alone across the stamp.
The top postmark is classified as Code SLKts (37×3)
The bottom postmark is classified as Code SLKb (32×4)
So how is an SL marking different from an SLK marking?
Code SLP
“SLP” is a Straight Line Postmark, with the date added by a separate stamp.
The following postmark is classified as Code SLPb (46×5)
