The following postmark is classified as Code SL3bs (46x2)
"SLK" is a Straight Line Killer, struck alone across the stamp.
The top postmark is classified as Code SLKts (37x3)
The bottom postmark is classified as Code SLKb (32x4)
So how is an SL marking different from an SLK marking?
"SLP" is a Straight Line Postmark, with the date added by a separate stamp.
The following postmark is classified as Code SLPb (46x5)
