Hey there.
This was actually planned to be a video tutorial, but then I found myself not being confident enough in my English speaking skills and I didn't want to edit text to a video with music. This "technique" obviously works with other buffs you gain, just replace 'Sword and Board'.
This tutorial does not teach you how to install addons, I therefore assume that you already have Mik's Scrolling Battle Text installed.
This is very simple so I will not make this too fancy and explain everything needed.
1. Open up the MSBT configuration by typing in /msbt
2. Go directly to Triggers and hit the "Add New Trigger" button. Choose an Output message, it's the text that will be shown when your SnB proccs. This is editable later if you get bored of yours.
3. The little white square decides about the color of your text warning. Use what ever you're comfortable with, maybe some signal color like red.
4. Click the

, I think that is called a cog. Make sure it's set like in the picture.
Most of the stuff should be like that by default. Simply click the screwdrivers to the left of the 2nd condition and change 'Unknown' to 'Sword and Board'. I do believe that that is case sensitive so watch out for that.
5. Save that. The

is optional, it's to set the size and the font of your text. MSBT accesses SharedMedia so if you want more fonts you should look into that.
6. 
, the 3rd button. Again some interesting options.
Output Scroll Area sets on which scroll area your notification shows up. You can look them up under 'Scroll Areas' and if needed add your own.
Output Message, again very obvious change it to what you like.
Sound, you can use the standard one but you can also add your own, there's a sound folder inside the MSBT addon folder.
'Always Sticky' modifies the way the text shows up a little, it makes it a little more visual and it stays longer that way. Personal choice, you got to test.
'Icon Skill'. Here you can enter the ID of a spell and it's logo will show up to the left of your notification. To find out about Spell IDs, go to wowhead.com, look up the spell and copy the numbers from the end of the URL.
7. Done. This should be it.
I hope this covers everything, as you can see it's really not hard. If any questions come up, fire at will.