I've made a dew of these to different designs, so forgive the mish-mash of photos in this instructable.
I make these up to order at www.zero-waste.co.uk
Step 1: What You Need
1 x reel of thick thread, preferably synthetic and a needle.
A pair of scissors, pen or chalk and a ruler and square.
This .svg layout sheet
Some Dress pins
A sewing machine.
Optionally: sew-on velcro. (approx. 1m per badge)
UPDATE - Have had to remove the .svg file link from here as apparently it never worked! See the link above for the .svg layouts.
Step 2: Choose a Design and Mark Out
Marking out is the trickiest bit, as one has to assess how best to cut up the vest. There's no real formula for this, I try to make use of the mesh and reflective strip as it is such that the minimum number of cuts and joins are required. Work out the best strategy on the paper by drawing on lines for the joins. You will want to add on 10mm around all the edges to allow for seams. Measure the dimensions, add on your 10mm and mark out on the vest using a pen/chalk and a ruler and square.
Step 3: Cut Out and Do a Dry Run
Step 4: Assemble
Continue in this fashion to assemble the whole badge. This stage takes a while and is very methodical, so be patient and don't rush.
Step 5: Hem the Outside Edge
At this point, if you would like the badge to be easily removable, sew on some velcro. I would put the hook side on the badge so that the bag or clothing remains soft when the badge is not attached. It is best to affix velcro all around the perimeter of the badge if possible to reduce sagging.
Step 6: Attach to the Bag or Clothing
I pin on the badge or velcro strips and use a backstitch or a zig zag running stitch around the edge. Be sure to tie off securely. Now is the time to add a label if you like, which looks quite good on the reflective grey strip material (see pic). For the velcro option, the method is all the same, but just sew on the looped velcro.