Classtimer does it.
Add a custom timer with the name of the buff that your trinket procs,
drag the sample bars to the middle of your screen/somewhere noticeable (mine's above my castbar)
and bam, job done.
You can also use Tellmewhen (it's spelled exactly like this) to do it. It shows up like the icon of the trinket proc and u can make it as big or small as u want and make it appear on the screen wherever u want. (This addon is also great for tracking talent/spell procs cooldowns, and can be used as a dot timer)