What do the black crosses on a vero layout mean?

Those solid black crosses you're seeing are almost certainly connection points or tap-off markers for external signal paths or power inputs, definitly not a track cut or a jumper jump. When folks are doing custom layouts from detailed schematics, expecially those that involve complex external wiring like switching or power, they often use specific markers that aren't standard for the routing itself. The cross at the top, near row K, where you mentioned it is, looks like a classic point where a main signal line needs to be tapped off to feed an external component or an LED array that isn't shown directly on that specific section of the trace. It’s a designation telling you to treat that location as a connection hub, not just another point in the routing flow. It’s not a polarity marker for diodes or anything like that, and it doesn't relate to the red squares you might see elsewhere. It’s purely a routing instruction. Since you are building a filter, those specific points on rows K and L are probaly where the main signal path needs to interface with the control circuitry or the external power rail. If you were to cut the trace there, you'd likely lose the intended signal continuity for whatever component is connected off-board. I ran into this convention once when working on a modular synth patch where the power distribution needed to be tapped into a specific signal ground point. The symbol was used to identify the precise point of integration. For your layout, assume those crosses mean you should run a trace to those points and establish a connection there, rather than treating them as just another point in the series of standard solder dots. It tells you a specific action to take regarding the signal's relationship with the outside world, not how to move the trace itself.

I think the cross mark is meant to indicate a point where you absolutely need to break the trace and physically solder off a lead to another component, like a jumper or a specific IC pin. When I was building a complex VC filter a while back, I used a specific set of small jumper wires and a set of tiny flush blade scissors to make these off board connections. It made a huge difference in how cleanly the signal fed into the module. It felt like the schematic was telling you, 'Don't just solder on here, physically split the circuit here.' If you just soldered a lead across without breaking the original trace, the signal might leak thru when the whole board is powered up.

So if I treat that cross like a spot to add a lead, does that mean I just run a wire right over it, or do I have to peel back the protective paint stuff first? I'm not really comfortable peeling back the solder mask on a board I just bought. Also, since it's a filter board, will that specific connection point affect the actual sound or will it just be for the lights on the front panel? I'm worried about ruining the signal if I mess up that part.

I agree with the idea that it means you need to physically break the trace and solder a lead off, just like the second person mentioned. When I was putting together a complex synth modulation circuit, I ran into this exact problem with the layout schematic. If you just run a wire over the symbol without breaking the existing trace, you risk a short against the wrong part of the signal path. My experience showed that the best way to handle it was to solder a tiny piece of bare wire directly into the existing trace at the cross mark, then insulate that lead with a bit of heat shrink before continuing the main signal to the component.

Update: traced the schematic and the first reply was right, those crosses are tap-off points for the off-board power wiring. Confirmed it once I followed the tracks back. Still stuck on the physical side though, like the third poster said, do I just solder the lead right on top of the existing track, or does it need scraping back first? Never done a tap like this before.