The symbols will be on the bottom of the combo filter cap. It just tells you which lead comes from where. Most filter caps are 40/ 60 or 80 for example so it matters what connects to where. In your case, it doesn’t matter as they both (the triangle and Box) are the same value (10 MFD) You will see this system of identifying the leads on other filter caps quite often on other radios.
The symbols are often found on the bottom of the container that holds the filter caps as Gary said; however, they are also often found on the sides of the container and I find they are usually more helpful than looking on the bottom as the symbols can be obscured by wiring.
On this particular schematic they are labelled as C31 and C32.
On some schematics they would be (for example) C31a and C31b.
This notation would indicate that both caps are in the same physical container and the symbols on the conatiner would help distinguish which cap is which.