Step 1: Identify the concept being tested.
The question asks to identify and explain an external source of recruitment used in the given situation.
Step 2: Explain the concept.
External sources of recruitment mean the company looks for candidates outside its own existing staff, and different situations call for different external methods such as direct recruitment, employment exchanges, placement agencies, campus recruitment, and advertisements.
Step 3: Apply the concept to the facts of the case.
The site supervisor placed a notice right at the entrance of the construction site asking daily wage labourers to report in person with identity proof, this is a direct approach where the notice is put up at the workplace itself and interested people simply show up to be selected on the spot.
Step 4: State the final answer.
This is Direct Recruitment. Under this method, a notice giving job details along with the date and time for selection is displayed at the factory gate or worksite, interested candidates gather at the given time and are chosen right there, making it a quick and inexpensive way to hire, especially suited for short term or urgent labour needs like this one.