so to create the superman emblem we use a simple trick
add a diamond from the basic shapes
on the left side you can see all

remove the group and delete the sparks

select the vector tool and move along the lines
when you have completed a lap click on the last point to close it
now you can move all the points so that they fit
when you are finished select the newly created shape and the diamond
and click on substract
now only the superman emblem is over
( i love little tricks to get to your goal)

For the Super i use the font Impact

for mom i use the font dancing script

adjust the fonts so that they stand out a little above the emblem

click on outline and set to 2
this varies from font to font 

select the outline and the emblem and click on substract

once both lines have been created, select everything and add it to a group

select everything and select outline again
do not set this too high 
you can see that small areas are created inside here
we simply remove these with the node function
click on edit node and select the nodes and delete them
either click on a node and hold the delete button until everything is gone 
or you select all nodes with the mouse and then delete them
the usefulness varies from situation to situation