They're supposed to be all asymptomatic to be part of the mass testing in Liverpool. That's the criteria for taking part (though I guess some may have sore throats, gastro symptoms, etc - ie not the 3 core Covid symptoms)
If the people taking part in the mass testing are typical of the whole population in Liverpool then that would suggest 3,500 people currently have Covid in Liverpool (0.7% of the 500,000 population). Around 1,400 have tested positive with symptoms in Liverpool in the last week, which suggests the majority (circa 70%) of people with Covid don't have any symptoms (or at least not the 3 key symptoms needed to get a test).
It may be, though, that the people queuing up for mass testing are those who're more likely to have it. There wouldn't seem much point in being tested if you, say, live alone and work from home. So the number of asymptomatic people across the entire city could be lower than 3500.
They've some way to go to test the whole city though if they've only managed less than 5% so far!