Signpost used enormous search engines but also employed human representatives to deal with inquiries. The representatives answered calls and directed callers to people who could help them.
Vishesh Abeyesekere and Pearl were stationed on the Moon when the Sixth Doctor's TARDIS interfered with the Signpost search engines. They developed a symbiosis with Signpost's search engines due to the influence of the TARDIS. (PROSE: Outsourcing)