Glad you asked, Cubalz.
Using the water tower picture name I scrolled through Word fonts until finding one with a similar capital letter I, finally settling on a bolded Ebrima font. I used Word Letter Art vertical for a perfect up-down alignment and spacing, experimenting with different font sizes and stretching the letters (used a lot of scrap paper print outs) until getting a reasonable “look and feel” match with the picture lettering. For the shamrock design, I used a shamrock paper plate cutting out one closest to the water tower size, using it to trace around on final stencil.
I then carefully cut out around everything with a new Xacto blade on a bread board to insure a clean cut. For the letter O, I left several connector slivers to keep the O’s center in place.
I then sprayed the stencil back with 3M Scotch Spray Mount #6064 which is the same glue used for Post It notes. I let it dry for several minutes to maximize the stickiness then applied to my model, repositioning several times until straight. I let it dry for 24 hours, rolling the tower back and forth on table top several times to insure letter edges were tight, then removed the connector slivers from letter O center after 24 hours.
I used the very softest hair non-nylon non-streaking brush to apply the contrast paint with one stroke downward and let dry. About 8 hours later I re-pressed all edges then repainted with one pass in opposite direction. I repeated this up-down pass sequence about 5-6 times until satisfied the lettering was covered with no obvious bleed throughs (I was in no hurry. 
) I removed the stencil and found all letter edges crisp. Using a very fine one bristle brush, touched up a few missed bleed throughs.
Granted, this was a long and tedious method, and experienced model will no doubt have better/quicker ways, but I thought the process through on my own, without consulting any online or book resources for methods. I am very pleased with the results, plus given the tower is positioned towards layout far rear, any imperfections are not noticeable (unless you have binoculars. 
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