During one of their frequent get togethers Martha confessed to how worried she was about the long hours Clark had been forced to put in as Superman with the Justice League recently. It seemed every time you turned on the news or read the paper there was another story of how Superman had swooped in to rescue someone from criminals, super villains, or a natural disaster. She worried about what sort of toll all of this was taking on her son. Physically he was probably fine, but emotionally? Martha and the farm were the place Clark went to relax and be himself, not play the role of "superhero" or "reporter." Where he could pour out his troubles to a sympathetic ear and be comforted by his mother after the horrors he might see while trying to save lives. But Clark had been so busy that he had been unable to visit her in Smallville, and yet with all of his recent activity it would seem that now would be a time when he would need the chance to decompress the most.
Loki reassured Martha that he had access to the Watchtower and could go and check up on their son (he might not have permission to visit the Watchtower but he certainly had access). He would deliver Martha's well wishes and ensure that Clark was not overextending himself. While Loki could (and had) entered the Watchtower unseen he thought it prudent to make a more polite entrance in this situation. He wanted time to talk with his son and he also wanted to meet his son's friends (and determine that his sons playmates were not taking advantage of Clark's good nature and slacking off their own superhero duties. If so, woe betide the Justice League!)
So on this occasion he let his presence be announced by a cacophony of alarms, materializing in the center of the meeting room and standing calmly with a basket of Martha's delicious muffins dangling from one arm while the League assembled.