This is completely untrue. The EU's accounts have been "signed off" every year since 2007.
You can see the words "signed off" for yourself:
2017: "We are therefore able to give a clean opinion on the reliability of (i.e. 'sign off') the accounts"
https://www.eca.europa.eu/Lists/ECADocuments/auditinbrief-2017/auditinbrief-2017-EN.pdf#page=12
2016: "We were therefore able to give a clean opinion on the reliability of (i.e. 'sign off') the accounts"
https://www.eca.europa.eu/Lists/ECADocuments/auditinbrief-2016/auditinbrief-2016-EN.pdf#page=10
2015: "We were therefore able to give a clean opinion on the reliability of the accounts ('signed off')"
https://www.eca.europa.eu/Lists/ECADocuments/auditinbrief-2015/auditinbrief-2015-EN.pdf#page=11
2014: "We were therefore able to give a clean opinion on the reliability of the accounts ('signed off')"
https://www.eca.europa.eu/Lists/ECADocuments/auditinbrief-2014/auditinbrief-2014-EN.pdf#page=10