Can mobs spawn on signs? “Yes,” the mob spawn are able to sign.
Inside frames, pressure plates, and other non-opaque blocks, individual monsters can spawn, whereas packs can not. They need a block in the center completely.
Since a whole pack tends on one level, there should be air blocks above a smooth surface to allow monsters to show up on it, and more air blocks will always allow more spawning.
New players will appear in the beginning in a small area surrounding the spawn point when the server is not in adventure mode.
This region is by default 21 x 21 blocks but can be changed using the single and multiplayer spawn radius.