Possible Clues:

• B'way showing
• Stamp feature, in philately lingo
• Ideal, in teenspeak
• Ideal, informally
• Hole, in philatelic jargon
• Certain border, to a philatelist
• Line to tear along: Abbr.
• Dotted line, at times: Abbr.
• Philatelist's concern, briefly
• Stamp feature, to philatelists