Time Machine backup on Mac OS X is indicated by the spinning icon in the Time Machine menu extras and the sound of the backup disk churning. No other notification is available on a standard system.
While some may not mind this lack of indication, I personally feel more secure knowing when my files are being backed up in real-time. For this reason, I would suggest using a third-party software with more clear-cut notifications, such as Carbon Copy Cloner.
Overall, Time Machine is a reliable option for Mac users looking to backup their data, but if you're someone who values constant reassurance, it may not be the best fit.
Version 1.0.1: N/A