The text is a play on the common computer command 'CTRL + ALT + DEL', which is used to interrupt a computer operation. However, it humorously suggests using this command to perform an unrelated action, reading a message, which is not a function of the command. This is not a pun as it does not exploit different meanings of a word or similar-sounding words.
Press < CTRL > < ALT > < DEL > to read the next message . . .