This 154 Lynchburg / Made in No 44 USA has either SDP or RDP which have been ground down. From the feedback I've gotten, here are the working theories: 1. Doorstop (most likely) 2. Uniform underpour (unlikely - drips show abrasion) 3. Slumper when glass was still semi-pliable (unlikely - drips show abrasion) 4. Pin drop due to weathering, insulator rubbed on crossarm (unlikely - drip abrasion too uniform) 5. Deliberate alteration pre-service or during service (unlikely. For what purpose?) 6. Deliberate alteration after service (unlikely. This would take a lot of effort - for what purpose?)