A UriSignature (as it relates to LLUP/BLIP messaging) is a URI that can be used to specify a person/place/thing in which the content is directed towards. It's important to understand that this URI does not represent a message delivery endpoint, and instead a way for a BLIP Messaging aggregator to sort and aggregate incoming messages. It is up to the owner of any given URI signature to physically subscribe/unsubscribe to the BLIP message feed made available by any given aggregation service.

In other words, the LLUP protocol does not provide any guarantees of message delivery, only the possibility that the intended recipient will be given notification of the existence of the message at which point they would choose whether or not they want to access the content the message points to.

For those interested in guaranteed delivery of a BLIP message, please reference the XMPP specifications, in particular [ RFC 4622:Uniform Resource Identifier (URI): Generic Syntax].