GP 2013 added Fixed Asset Auto Numbering. In Fixed Asset Company Setup you can now choose to auto number books and set the numbering sequence in the Next Asset ID field.
Weekly Dynamic: GP 2013 Fixed Asset Auto Numbering
Tips & Hidden FeaturesGeneral Ledger & FinancialsGP 2013
Archived post from 2013. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.