I have just created warm and cold front markers for meteorological charts.
It may be useful to someone, even if just as an exemple on how to create markers.

This is the code I grafted in my /usr/share/inkscape/markers/markers.svg :

<!-- fronts -->
<marker style="overflow:visible" id="ColdL" refX="0.0" refY="0.0"
orient="auto" inkscape:stockid="ColdL">
<path transform="scale(1.2)"
style="fill-rule:evenodd;stroke:#0000ff;fill:#0000aa;stroke-width:1.0pt;marker-start:none"
d="M -3,0 L 0,4 L 3,0 L -3,0 z "/>
</marker>
<marker style="overflow:visible" id="ColdM" refX="0.0" refY="0.0"
orient="auto" inkscape:stockid="ColdM">
<path transform="scale(0.8)"
style="fill-rule:evenodd;stroke:#0000ff;fill:#0000aa;stroke-width:1.0pt;marker-start:none"
d="M -3,0 L 0,4 L 3,0 L -3,0 z "/>
</marker>
<marker style="overflow:visible" id="ColdS" refX="0.0" refY="0.0"
orient="auto" inkscape:stockid="ColdS">
<path transform="scale(0.4)"
style="fill-rule:evenodd;stroke:#0000ff;fill:#0000aa;stroke-width:1.0pt;marker-start:none"
d="M -3,0 L 0,4 L 3,0 L -3,0 z "/>
</marker>

<marker style="overflow:visible" id="Cold2L" refX="0.0" refY="0.0"
orient="auto" inkscape:stockid="Cold2L">
<path transform="scale(1.2)"
style="fill-rule:evenodd;stroke:#0000ff;fill:#0000aa;stroke-width:1.0pt;marker-start:none"
d="M -3,0 L 0,-4 L 3,0 L -3,0 z "/>
</marker>
<marker style="overflow:visible" id="Cold2M" refX="0.0" refY="0.0"
orient="auto" inkscape:stockid="Cold2M">
<path transform="scale(0.8)"
style="fill-rule:evenodd;stroke:#0000ff;fill:#0000aa;stroke-width:1.0pt;marker-start:none"
d="M -3,0 L 0,-4 L 3,0 L -3,0 z "/>
</marker>
<marker style="overflow:visible" id="Cold2S" refX="0.0" refY="0.0"
orient="auto" inkscape:stockid="Cold2S">
<path transform="scale(0.4)"
style="fill-rule:evenodd;stroke:#0000ff;fill:#0000aa;stroke-width:1.0pt;marker-start:none"
d="M -3,0 L 0,-4 L 3,0 L -3,0 z "/>
</marker>
<marker style="overflow:visible" id="WarmL" refX="0.0" refY="0.0"
orient="auto" inkscape:stockid="WarmL">
<path transform="scale(.6)"
style="fill-rule:evenodd;stroke:#ff0000;fill:#aa0000;stroke-width:1.0pt;marker-start:none"
d="M -3,0 A 3,3 0 0 1 3,0 z"/>
</marker>
<marker style="overflow:visible" id="WarmM" refX="0.0" refY="0.0"
orient="auto" inkscape:stockid="WarmM">
<path transform="scale(.4)"
style="fill-rule:evenodd;stroke:#ff0000;fill:#aa0000;stroke-width:1.0pt;marker-start:none"
d="M -3,0 A 3,3 0 0 1 3,0 z"/>
</marker>
<marker style="overflow:visible" id="WarmS" refX="0.0" refY="0.0"
orient="auto" inkscape:stockid="WarmS">
<path transform="scale(.2)"
style="fill-rule:evenodd;stroke:#ff0000;fill:#aa0000;stroke-width:1.0pt;marker-start:none"
d="M -3,0 A 3,3 0 0 1 3,0 z"/>
</marker>
<marker style="overflow:visible" id="Warm2L" refX="0.0" refY="0.0"
orient="auto" inkscape:stockid="Warm2L">
<path transform="scale(.6)"
style="fill-rule:evenodd;stroke:#ff0000;fill:#aa0000;stroke-width:1.0pt;marker-start:none"
d="M -3,0 A 3,3 0 0 0 3,0 z"/>
</marker>
<marker style="overflow:visible" id="Warm2M" refX="0.0" refY="0.0"
orient="auto" inkscape:stockid="Warm2M">
<path transform="scale(.4)"
style="fill-rule:evenodd;stroke:#ff0000;fill:#aa0000;stroke-width:1.0pt;marker-start:none"
d="M -3,0 A 3,3 0 0 0 3,0 z"/>
</marker>
<marker style="overflow:visible" id="Warm2S" refX="0.0" refY="0.0"
orient="auto" inkscape:stockid="Warm2S">
<path transform="scale(.2)"
style="fill-rule:evenodd;stroke:#ff0000;fill:#aa0000;stroke-width:1.0pt;marker-start:none"
d="M -3,0 A 3,3 0 0 0 3,0 z"/>
</marker>

i dont get it. Do you want to say you _wrote_ an svg picture? Standing ovations to you.