A short code is often associated with an automated texting service such as DialMyCalls. It can handle the response and typically requires the sender to start the message with a command word or prefix. The service then responds to the command appropriately.
In ads or in other printed material where a provider has to inform about both the prefix and the short code number, the advertisement will typically follow this format:
Example - "Text 'AWESOME' to 80123 for awesome news every Friday." (80123 is the short code in this example)
When a text message is received from the DialMyCalls short code (80123), replying with the word "STOP" will automatically remove that recipient from receiving any further text message from that particular short code - texting the word "START" to the short code will remove them from the Do Not Call list and their text message alerts will start back up again.