What do you use to write on fondant?

I made a fondant covered cake this past weekend and after writing the birthday message on it, noticed that the buttercream was seeping/bleeding into the fondant.

I'm pretty sure I'm the only one who noticed. Would royal icing be better to prevent this? My concern would be getting it the right consistency.

I only use royal icing for piping on fondant. I know some people use meringue powder and all sorts of different recipes, I just go basic though. For piping and whatnot I just use egg whites and powdered sugar to the desired consistency (too runny, more PS, too stiff, more egg whites. It's not an exact science). I only add corn starch & cream of tartar when I'm "building" things (gingerbread houses, pastillage showpieces, etc.).

Using royal icing on fondant is usually the best way to go for the reason you stated. The oils from the buttercream start being absorbed by the fondant and it doesn't look quite right.

HTH

Michele