What is Incident no.? (WD Black 1TB)

I have to send a mail to WD about a hard disk I bought. It is WD Black and the website is showing 2 years warranty instead of 5yrs.

The mail I received from WD is

Your subject of your email should be,' Proof of purchase for Western Digital'.

The body of your email should consist S/N#, MDL#, Date of Purchase, Incident #

Click to expand...

But I don't know what Incident# is.