What are the square brackets in the flash message content?

First of all, Flash Messenger is based on USSD (Unstructured Supplementary Service Data), which is an unstructured supplementary data service. It is a new type of interactive data service based on the GSM network. From the perspective of application in the current scenario, Flash Messenger is an information push service based on mobile phone screen pop-ups; it can meet the application needs of various enterprises in many fields such as customer service and information release

Others 2. USSD flash message is a new SMS service. USSD flash message is sent and displayed directly on the mobile phone screen. It has the feature of forcing the recipient to read. At the same time, the mobile phone user needs to click to confirm before performing other operations. When the flash message is sent, it includes signature + content. The contents of the parentheses mentioned by the poster are actually the signatures for users to uniformly use this mechanism and report uniformly.

So, the suffix mentioned by the poster is actually the signature of Baidu Mobile Guard!