The act of tuning is adjusting fuel and ignition tables to optimize the parameters for the particular application of the engine.
For tuning, there would be some sort of system in place to accomplish this. These range for the cheap and lousy way of doing it with a FMU and AFC combo, which is an dangerous/cheap/inaccurate way of doing it, to systems such as Hondata, Neptune, Chrome which consist of an EPROM installed into the ECU and tuning software to control it and are much more precise, accurate and capable of controlling much more. Then there are the full standalone units which essentially replace the factory ECU with one designed outright from day 1 to allow for full control over all engine functions and parameters
For it to be tuned, one of these methods must be in place. If there is a method of tuning installed, knowing whether it has been tuned or not is hard to say. If it runs like shit, stumbles, bogs or had any sort of issues of misfiring nature leading to a lumpy/jerky powerband, then it has not been tuned (or not worth a damn)
Knowing the extent/quality of a tune can really only be identified for certain through datalogging. An educated and experienced mind can tell how the adjusted parameters are working for the engine through reviewing datalogs.