Assess the specific activities under destination rules and effective immigration authorization. Do not assume that avoiding signature makes all other fieldwork permissible. Have the proposed initial tasks reviewed before the employer schedules the first assignment.
Agree the permitted scope before dispatch
Record any limits and ensure the person assigning field tasks knows them. If the assignment expands, review the change before carrying it out. The plan should reflect real lawful work rather than a temporary description of duties the applicant cannot yet perform.
The question is not whether work can begin but which work. Sort the proposed first tasks into three lists: activities that plainly require the destination registration, activities that plainly do not, and activities nobody in the room can confidently place. The first list waits.
The second may proceed once immigration authorization is actually effective, meaning admission or approval rather than a submitted application. The third list is the one that causes trouble, and it belongs in a written question to the regulator rather than in a supervisor's judgement. Hypothetical example: a crew is asked to run control and provide layout for a signalling equipment installation while the responsible surveyor's registration is still pending, on the reasoning that nothing is being certified.
Whether that is permissible turns on the destination rules for those specific acts rather than on the absence of a signature, and it can be asked in advance.