The thing is, signs can be placed but not read. I can read it while I am typing it, but when the keyboard goes away, so do the words on the sign. One weird thing is, if I go up real close to the sign and it is at eye level, I can make it out. But that is the only time I can. Please fix, thanks!
If you have not already, I recommend performing a search before submitting a ticket as it is likely your bug has already been reported.
This issue was reported previously as MCPE-6450, comment your experience there!