I started looking at Amazon's Trademarks for the word Echo and here are a few I found. I'm not sure if they apply or not but some of them sound very close to podcast related:

http://tmsearch.uspto.gov/bin/showfield?f=doc&state=4807:3pl...

http://tmsearch.uspto.gov/bin/showfield?f=doc&state=4807:3pl...

http://tmsearch.uspto.gov/bin/showfield?f=doc&state=4807:3pl...

http://tmsearch.uspto.gov/bin/showfield?f=doc&state=4807:3pl...

http://tmsearch.uspto.gov/bin/showfield?f=doc&state=4807:3pl...

http://tmsearch.uspto.gov/bin/showfield?f=doc&state=4807:3pl...

http://tmsearch.uspto.gov/bin/showfield?f=doc&state=4807:3pl...

http://tmsearch.uspto.gov/bin/showfield?f=doc&state=4807:3pl...

http://tmsearch.uspto.gov/bin/showfield?f=doc&state=4807:3pl...

http://tmsearch.uspto.gov/bin/showfield?f=doc&state=4807:3pl...

http://tmsearch.uspto.gov/bin/showfield?f=doc&state=4807:3pl...

http://tmsearch.uspto.gov/bin/showfield?f=doc&state=4807:3pl...

http://tmsearch.uspto.gov/bin/showfield?f=doc&state=4807:3pl...

http://tmsearch.uspto.gov/bin/showfield?f=doc&state=4807:3pl...

http://tmsearch.uspto.gov/bin/showfield?f=doc&state=4807:3pl...

http://tmsearch.uspto.gov/bin/showfield?f=doc&state=4807:3pl...