That is an encrypted private message. You should be able to read it inside your wallet if steemit.com has your private memo key. Here some more technical information about it :
https://steemit.com/steem/@dantheman/how-to-encrypt-a-memo-when-transferring-steem
Perhaps encrypted memos ought to have a header like "---Begin PGP signed message---" before the encrypted text like the way encrypted emails do it?
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