This website can be used to generate logo.rle files.
Usage:
http://graciarnia.halamix2.pl/pmos/logo_test/?height=<x>&width=<x>
http://graciarnia.halamix2.pl/pmos/logo_test/?height=<x>&width=<x>&preview=png – shows png preview, also availiable: png, bmp or jpg, example below uses jpg for faster load times.
&text=<yourtext> – experimental feature, may not work as intended, this is quick and dirty solution after all

You can also type http://graciarnia.halamix2.pl/pmos/logo_test//logo-<width>x<height>.rle
.png, .jpg and .bmp files are also available this way

postmarketOS logo file is licensed under a Attribution-ShareAlike 3.0 Unported license
source code
Example: