... or any water-drop-ish kind of shape, for that matter. Freehanding a nice, mostly symmetrical blood drop shape is not an easy thing to do with a brush, and it's even more difficult to make sure that drop is in exactly the right place, so here's an easy way to make it happen that I've been using for years on my Blood Angels. Firstly, you have to get out your fine detail brush and draw an inverted cross:
It doesn't have to be perfect, all you need is to make sure each tip of the cross clearly marks the position of the desired blood drop, i.e. .
Breathe slowly and draw in those lines marked in yellow. From then on, all you do is fill in your blood drop and viola!
For a large-ish area like this Land Raider's door, it's usually best to use multiple thin layers until you get a nice, solid coat. I like adding in little scribblings of white text (coz the Astartes do love their inspirational words) so I'd dab in those lines there while waiting for each coat to dry on the big drop.
Suffice it to say, practice makes perfect. I for one have used this trick a few dozen times on my rank and file Marines, and certainly prefer it to fiddling about with decals.