AFAIK there is no direct and straightforward way to tell whether the current user is an administrator or not. After a bit of fiddling around, I was able to find a command that did the trick when combined with a few other measures and values.
[MeasureUserName]
Measure=Plugin
Plugin=SysInfo
SysInfoType=USER_NAME
IfCondition=1
IfTrueAction=[!CommandMeasure MeasureGetLocalGroup "Run"]
[MeasureGetLocalGroup]
Measure=Plugin
Plugin=RunCommand
Parameter=net localgroup Administrators
OutputType=ANSI
FinishAction=[!EnableMeasure MeasureUserAdmin][!UpdateMeasure MeasureUserAdmin]
[MeasureUserAdmin]
Measure=String
String=[MeasureGetLocalGroup]
IfMatch=(?s).*\b[MeasureUserName:EscapeRegExp]\b.*
IfMatchAction=[!Log "User '[MeasureUserName]' is an administrator"]
IfNotMatchAction=[!Log "User '[MeasureUserName]' is not an administrator"]
DynamicVariables=1
Disabled=1
This code retrieves the current username, then runs a command that lists all users in the "Administrators" user group. The third measure runs that command output through Regex to determine whether the given username is included in that group. The regex ensures a match only if the exact username is by itself (its own word). For example, if the username is 'Ben', who is a standard user, and there is another user 'Benjamin' who is an admin, the regex will not misidentify 'Ben' as an admin.