You can achieve a very nice subtle pattern effect on the bottom of your FDM 3D prints with this easy trick.
Make sure you can print smooth first layers - in my experience the best first layers can be achieved when you slow your speed waaaay down, like 10mm/s slow.
This trick works best on smooth print surfaces, preferable ones that are scratch free. I haven't tried on other surfaces, but in theory it should also work on rougher ones too - let me know if you try!
Step 1: Clean Your Print Surface
First, we need to make sure all surfaces are clean and smooth, with no residue.
To achieve this, use some good old isopropyl alcohol. I keep mine in a spray bottle for easy application. Spray it all over, somewhat generously. Leave it soak for a few moments and then wipe it clean with a cloth.
Using a cloth instead of paper towel is the way to go since paper towels can be abrasive and contain a lot of fiber that can leave a lot of debris on the surface.
Step 2: Apply Hairspray on the Print Surface
Hairspray is a wonderful thing for FDM 3D printing! It sticks well, leaves an even, thin layer when applied, and smells good too when you heat up your heated bed :)
Make sure to spray an even layer to your surface. If your bed plate is removable, even better, remove it and keep the spray can at a perpendicular angle to the surface. You can then fan it a bit for a quick dry.
Step 3: Print a Pattern
Now that we have a freshly coated surface, we need to print a pattern on it.
Use your favorite 3D design software to create a pattern you like and export a one layer (0.2mm) thick STL. I designed the pattern in Adobe Illustrator, exported an SVG, then used Fusion 360 to extrude the shape and create the STL file. There are many ways to do this, use what you are comfortable with.
Once you have it sliced, proceed to print.
Step 4: Remove Pattern Print
Once the pattern is done printing, remove it carefully from your surface.
You should see a visible mark where your filament was before, if it looks spotty or uneven, you can repeat the print until you see nice even mark after removal. Make sure to print it on the same exact spot though.
Step 5: Print Something Cool!
Now that your surface is ready and prepped, go ahead and print your object you want the pattern to show up on!
Easy as that. Have fun!