Patrick McDonnell, creator of Mutts seeds his comic strip with vintage pop culture references. Some of subtle, some obvious -- but all are great fun. January 29, 2014, he folded one of his running gags into a brilliant reference to George Herriman's Krazy Kat. (click on image to enlarge)
Those two squirrels have been bouncing acorns off of noggins for some time now -- and the victims haven't always been characters within the strip (The Mighty Marvel Mutts). In this case, it's the context that's the cameo.
It's an amusing sequence for the casual reader. I think that's probably why McDonnell chose to spell Krazy Kat the standard way -- using the K's would have been confusing for someone who wasn't familiar with Herriman's work.
Comics fans, I think, got more enjoyment from this sequence. Krazy Kat revolved around the odd relationship between Ignatz the mouse and Krazy Kat. Ignatz throw bricks at Krazy Kat, which Krazy would interpret as signs of love. As you can see from a typical Krazy Kat panel, McDonnell's sequence is spot-on. And the punch line is almost a knowing wink of the eye to comics lovers.