A number of the alert parameters allow you to insert a variable which will be substituted for a value when the alert happens. Here is a list.
$host
Host name (or IP address, if no name exists).
$hostip
The host IP address
$hostdnsname
The resolved DNS name for the host
$year
Current Year
$month
Current Month
$day
Current day of month
$hour
Current hour
$minute
Current minute
$second
Current second
$date
Same as $year-$month-$day.
$time
The same as $hour$minute - note the absence of any punctuation - that's to make sure the file name is valid, if this mask is being used in a file name.