If Salesperson Reid's billboard did not clearly identify Reid's employing brokerage, what action might the Registrar take?

If Salesperson Reid's billboard did not clearly identify Reid's employing brokerage, the Registrar might take action by requiring an acknowledgment and undertaking. This means that Salesperson Reid would be asked to acknowledge the mistake and provide an undertaking to rectify the situation by ensuring proper identification of their employing brokerage on the billboard in the future.

Option A is incorrect because referring the matter to the local police department is not the typical course of action in this situation. Option B is incorrect as there is no mention of immediately suspending Salesperson Reid's registration for this particular issue. Option C is incorrect as issuing a Registrar's Notice of Proposal is usually done for more serious violations.

Option E is incorrect as requesting a formal apology is not a typical response to a violation of failing to identify the employing brokerage. Option F is incorrect as conducting a full investigation is usually reserved for more complex or serious cases.

Therefore, the most appropriate action in this scenario would be to require an acknowledgment and undertaking from Salesperson Reid.