Form 8283 only needs to be signed by the charity if you donate more than $5000 of non-cash items, or you donate certain other items that require an appraisal. If you have between $500 and $5000 of non-cash donations, you need to include the form with your tax return but it does not have to be signed.
I don't know when the paper form 8283 was available for download on the IRS web site, but probably much earlier than when the electronic form was approved for e-filing. In any case, if you have donations that require a signature, you should have made arrangements ahead of time with the charity and the appraiser, and they should not have a problem signing an updated copy of the form for you.
