In Dynamics GP Inquiries and Reports, an asterisk (*) on the end of a transaction number indicates a voided transaction. Most folks figure that out pretty fast. Less commonly known is that a pound sign (#) at the end of a transaction number indicates that this is an intercompany transaction using the standard intercompany functionality in Dynamics GP.
Weekly Dynamic: Identifying Intercompany Transactions
Tips & Hidden FeaturesGeneral Ledger & Financials
Archived post from 2010. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.