If some stellar civilization sent a space probe (say something similar to our Voyager probes in shape/size/materials and communication capability) and it ended up in a regular orbit around the Earth in something below geosynchronous orbit, would we be able to randomly detect it? This detection could be visually or via detection of RF emissions aimed towards its' origin location.
Small asteroids are occasionally, but routinely discovered, often just before or just after closest approach. For example a 3.5m asteroid 2021 RS2 was discovered at a MEO distance. It has a comparable size to Voyager but is probably darker.
So a Voyager probe in MEO would probably be picked up by asteroid scanning systems.
Once an orbit was determined, and it was found to be in Earth orbit, interest would pique, and people would become interested, spectra would be taken, and the spectrum of something artificial is very different from that of rock.