Possible Clues:

• Be obvious, and that it's in Guinness
• Conspicuous one
• It must be obvious that this is not a sit-in
• Protrude
• Be prominent and superior
• Protrude being fat in two parts!
• And a porter outside would be conspicuous
• And that's what's in Guinness to make it so distinctive
• And, carried by the porter, are easy to spot
• Be prominent or superior