Cycles alpha-texture on texture combination

Hey community,

I want to put an alpha masked texture on an other texture.
The only method I found was to combine two normal textures with two UV-maps and an attribute node, but as I said I just want an alpha masked texture on an other texture like a decal.
Hope for help :wink:

Sincerly,
ElGreco

I already know this post, but I want to work with an image texture with an alpha channel and if possible only one UV-layer

Edit: Sometimes it works, but I dont really understand it and I have an other problem.
I put an alpha channeled sign on a wall texture and now I want to scale the sign down, but always both textures scale.
I also dont understand the effect of the attribute node. It doesnโ€™t make any difference in my scene neither with it nor without.