Beyond this "residential area" sign, can you expect to see devices enforcing slow driving without warning signs?

In the video you are entering a narrow street in a small town; on the right there is a blue sign D-40 "residential area", and below it sign B-18 "3.5 t". Beyond this sign, devices that force slow driving might not be marked with warning signs. The answer is: yes.

The Regulation on road signs and signals states that sign D-40 "residential area" marks the entry to a residential area and also informs that devices and measures forcing slow driving placed in a residential area might not be marked with warning signs. This means speed bumps, road narrowings, chicanes and raised junctions - in normal traffic a speed bump is preceded by sign A-11a, but in a residential area this sign can be left out, because the driver must drive at no more than 20 km/h anyway and expect pedestrians across the whole width of the road. So sign D-40 itself is a warning: beyond it, you expect a speed bump around every corner. The Road Traffic Act adds that in a residential area a pedestrian has right of way over a vehicle, parking is allowed only in designated places, and when leaving the area you are joining traffic (włączanie się do ruchu) and give way to everyone. Sign B-18 below it prohibits entry to vehicles with an actual total mass of more than 3.5 t.

Legal basis: § 58 para. 1 and 2 of the Regulation on road signs and signals; Art. 20 para. 2 and Art. 11 para. 5 of the Road Traffic Act (Prawo o ruchu drogowym)