What is the significance of this symbol?

Further to Billy and Trevor's test-point suggestion, the test points may be designed for a pogo-pin test fixture and some special PCB "pad" assigned for the function.

Figure 1. A PCB test fixture with pogo-pins allows simultaneous and rapid connection to multiple points on the circuit. Source: Spehro Pefhany's answer to Is there such a thing as a pin (or pogo pin) clamp for testing?.

Such a system might, for example, allow automated testing of your power-supply board under various conditions such as lower and upper limits of the supply voltage, no-load, half-load and full load on the output and testing control inputs and monitoring outputs. When I first saw National Instruments equipment thirty years ago this seemed to be a large part of their business.

Figure 2. Pogo-pin test pads on a PCB. The quantity of test pads in this case suggests that the designer is not all that confident!

See What parts would one typically use for automated PCB testing? for more details and photos of pogo-pin types.

I would also guess these are test points.

Moreover, the test point may also include a via to bring a trace through to a pad on the other side of the board to facilitate one-sided testing. Looking at the schematic as a whole, there are a spattering of them but not on every trace. That suggests the other traces are already visible from the test side. These test pads are probably inserted by the PCB designer.