A logo needs to tell us something, so it's usually the company name and no caption. i.e. Samsung, Virgin Money, LG etc etc. A crest is basically a Coat of Arms.
Would you call this a logo, Mike?
http://upload.wikimedia.org/wikipedia/commons/thumb/5/5c/Great_Seal_of_the_United_States_%28obverse%29.svg/600px-Great_Seal_of_the_United_States_%28obverse%29.svg.png
Damn, man. You even use the words "crest" in the US. It's in the American English Dictionary...
http://clutch.mtv.com/wp-content/uploads/2012/02/tumblr_llmh57dwz71qj0zk3o1_500-1.gif