@nye For an account to be ‘flagged’ or set as being a Pattern Day Trader (PDT) then it must exhibit a pattern of day trading. What this means is the account must execute more than 3 day trades within 5 trading days.
So, simply place 4 or more day trades. These could be fractional shares. Something like this will get an account flagged PDT if done in a single day.
Note that one must have more than $25,000 in equity in the account. Also note the PDT designation is permanent (though there can be a 1 time exception to get it removed). So only get an account designated PDT if one can be sure to maintain more than $25,000 in equity.
Once PDT is set the account will see 4x daytrading margin the following day.