My Food entry for the Halloween Food Contest, they look like urinal deodorizer cakes, with a "P" added for effect.
Step 1: Ingredients
Blue food colouring
Icing/frosting in a contrasting colour to cake.
1 zip-lock bag for icing/ frosting use in case you don't have a piping bag.
Step 2: Mixing and Baking
Prepare cake mix according to instructions, when well mixed add Blue food colouring I used almost 1/2 a bottle, mix again until you get the blue thoroughly mixed in.
I used silicon muffin cups to cook them in in the muffin pan.
Bake following directions on the box, for cup cakes.
When done let cool for at least 45 minutes, remove muffin cups carefully.
Using a serrated knife cut off the muffin tops, place bottom of cup cakes upside down on a plate.
Step 3: Finishing
Cut a small corner off of the zip-lock bag, put in two table spoons of icing/frosting.
Squeeze icing/frosting towards open cutoff corner end of bag.
Practice writing on Muffin tops, when you get it right put a "P" on each of the "Urinal Cakes" .
Squeeze the rest of the icing/frosting onto muffin tops and eat them.
Note: I guess I ate too many muffin tops (4) I had Smurf poop the next morning, yes it was Blue, sorry about the toilet humor.