The main identifying feature is the bright yellow color of the mushrooms. The cap (pileus) in the young fruit-bodies is usually taller than broad, though becoming convex, often with shallow radial grooves near the margin, with maturity. There is a ring left on the stipe and the cap can be campanulate when mature.
Can cause significant stomach problems and is quite poisonous.
It has a tendency to pop up unexpectedly in people's flower pots--even indoors!
Leucocoprinus birnbaumii won't hurt you, unless you eat it. It won't hurt your plant. It won't hurt your pets or your children, unless they eat it. There is no getting rid of it, short of replacing all the soil in your planter (and even then it might reappear). Since it makes such a beautiful addition to your household flora.