If you are truly up for this challenge of painting it yourself, pick up your brush and let's do it!!
Each icon shown on previous White Dwarf or even codexes are different. Some maybe slimming, longer, sharper, wider, or larger.
For this tutorial, I followed icon designed from current Space Marine Codex.
1) Start with a straight stroke. Thicker line mean I pressed with my brush; thin sharp line mean I released my brush.*
2) 2nd stroke
3) 3rd stroke
4) 4th very short stroke for nose. And now joined it by painting it like fin.
*Your stroke can be from left to right; or right to left. Just use whichever comfortable. For me, I used right to left. Refer here for info on stroke line.
5) Paint the jaw
6) Paint 3 strokes for the last 3 lower fin
7) Join all of the 3 lower fin
8) Paint the jagged teeth.
9) Paint the eye with a triangular shape stroke.
10) Trimming the outline by using background color or fatten it by using the icon color (for this is white) until the shape you wanted. Refer here for info on trimming.
Viola!! There you go!! Easy!! You just need more practice and you will master it. You can add a ring as I've done above for my banner... or you can add a fiery background to make it a Fire Drake. Just refer my previous tutorial for more info, here.