Engraved mark is cut ito the glass with a point or similar. Acid etched also cuts into the surface and was often applied with a rubber stamp allowing quite complex mark designs. Some may have been etched by transfer. Mostly today, marks are sandblasted, often with an obvious stencil as it is cheaper and safer. For example, almost all Stuart Crystal has a sandblasted mark (since the 1970's ??guess?? ). Sandblasting can often result in a very faint and almost superficial mark.
All of those methods can be used by hand or semi/fully-automated. It is not always possible to tell which method has been used and no-one has published a definitive guide.
Soon to be ousted by ink-jet printed marks which may or may not use an etching compound and will allow for very complex designs that can be fired in.