Image transfers are magic to me. The ability to produce perfect lettering on a piece of wood without having to do it freehand is wonderful. There are many ways of transferring, but most use either heat or solvents which won't work on a painted surface. This will work. Think rub-ons.
Lori Barker helped me with this. You can view her fantastic artwork
here.
Materials
overhead transparency film
2 painted boards (9"x 12")
scotch tape
clear spray paint
carpenter's glue
Tools
ink jet printer
wooden stick (popsicle stick or bone folder)
drill

Download "All You Need is Love"
here or "Love is All You Need"
here. Print it using a borderless letter size on a piece of overhead transparency film. Set your print command to "transparency" or "glossy photo paper".
You can compose your own lettering and reverse it (important). The command for reversal in Photoshop is "flip horizontal". You need to save your image as a picture in Word then flip it (goggle for instructions). Some printers will reverse. Look for the commands of "flip, reverse or mirror" in your computer application.

The lettering on the film will be very wet when it comes out of the printer. Handle carefully. I heat the lettering with a hair dryer (a heat gun may melt the film) and let it sit for awhile.
Turn it over so that the printed side is down and lay it gently on your painted surface. Tape it in the middle of each side so that the film won't slip. Rub with your wooden stick. Lift to see if everything has transferred leaving the tape in place. Continue to rub until everything has transferred. Remove the film. The lettering will be gray.
The image is water soluble so any mistakes can be removed with a damp Qtip. If you accidently remove something you want to keep, place the film back on the surface and rub again. (it may work)
Start with a very light coat of clear spray to seal and protect the image. Spray several coats after the initial one is dry to fully waterproof.
Drill a hole partially through the middle of your board and insert the dowel from your carved heart, using carpenter's glue. Attach a sawtooth hanger on the back and let everyone know that you have a romantic soul and you like the Beatles.