[Holbein]

Apple's sign looks very much like an exit sign to me:

http://www.designofsignage.com/application/symbol/railway/la...

https://encrypted.google.com/search?tbm=isch&q=exit%20Pictog...

[smrq]

Yeah, it reminds me mostly of the MediaWiki outgoing link icon, which is used as an "exit sign".

[gdh73]

Interesting point. In a way, whatever you're sharing or sending is leaving your system.