I love the SIS: See If Starving
My equivalent is OID: Only If Desperate and I am relieved to say in 12 years I have never had to use it yet.. Usually means they are complete knobheads, utterly filthy dirty etc
I have another, HDWK: Hard Work, which usually just means they are physically very demanding, but generally clean, fresh and OK in personality
Often when a phone has blocked you, you hear a little half ring before voicemail kicks in.
Dead giveaway, but may not happen on all phones.