Help identifying an SMD component
These are 0603 zero-ohm resistors - the "O" is actually a "0". Basically it is a solder jumper or jumper wire but in a machine assembly friendly package.

On single-layer boards these are often used to assist routing and jump over traces. This appears to be the case for J2 and J3.

They are also frequently used for changing configuration pins. You typically have two resistor footprints, one to VCC and one to GND. On this you can place a zero-ohm resistor on either footprint to pull the configuration pin low or high. This is sometimes known as "strapping" and appears to be what OP3 is used for.