To be precise, we don't refer to DC as a signal since the word signal implies information content.
DC on circuit boards can suffer from AC coupling, but there are rules-of-thumb that every experienced designer uses to add filtering to the DC wires so that any AC that is accidentally coupled into the DC is automatically filtered away. The most common kind of filter to do this is the "bypass capacitor".
The amount of separation that you need between AC and DC depends on the amount of current in the AC. It is very important that you said the AC can be many amps (like 16) as this is a relatively high amount compared to most hobbyist's experience. The coupling between the copper traces is mostly inductive at these frequencies and inductive coupling is a function of current flow. The closer the traces are, the more inductive coupling. The more that one trace follows alongside another, in parallel, the more is the inductive coupling. If one trace crosses another at right angles, the inductive coupling is very low, so there is little risk compared to when the traces are side by side for some distance.