the software will simply say "BLOCK!!!" and you will know it, or you will simply see an incoming transaction of 25 btc to your core wallet, because you need to leave it open while mining in solo
You have to be quick seeing a
Block Found! message in between the other messages concerning the mining. Once you close the Miner program, there should be a summary of the mining values and the number of blocks found (if any). Good Luck, and keep us posted.