The ATMEGA256RFR2 Xplained Pro Evaluation kits has been certified for use in European Union countries. A Declaration of Conformity must be issued for each of these standards and kept on file as described in Annex II of the R&TTE Directive.
Furthermore, the manufacturer must maintain a copy of the modules' documentation and ensure the final product does not exceed the specified power ratings, antenna specifications, and/or installation requirements as specified in the user manual. If any of these specifications are exceeded in the final product, a submission must be made to a notified body for compliance testing to all required standards.
The 'CE' marking must be affixed to a visible location on the OEM product. The CE mark shall consist of the initials "CE" taking the following form:
The CE marking must have a height of at least 5mm except where this is not possible on account of the nature of the apparatus.
The CE marking must be affixed visibly, legibly, and indelibly.
More detailed information about CE marking requirements you can find at "DIRECTIVE 1999/5/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL" on 9 March 1999 at section 12.