What does it mean to have a SIC limitation on your medical class 1
This EASA document Easy Access Rules for Medical Requirements explains what the Specific Medical Examination (SIC - Medical Certificate Limitation Code) is and how it applies to medical qualifications for pilots/crewmembers). An explanation of what it means is found in the EASA document referenced above on page 52, item 8:
(8) SIC   Specific regular medical examination(s)   contact the medical assessor of the licensing authority.
This limitation requires the AeMC, or AME to contact the medical assessor of the licensing authority  before  embarking  upon  a  revalidation  or  renewal  aero-medical  assessment. The  limitation  is  likely  to  concern  a  medical  history  or  additional  examination(s)  which the AeMC or AME should be aware of prior to undertaking the assessment.
Apparently it means that when you go to revalidate or renew your medical certificate the AME will have to contact the medical assessor of the licensing authority and you will have undergo some additional testing or the AME will be made aware of some specific medical history or issue that needs to be considered prior to renewal or recertification of your medical certificate. Perhaps similar to having a non-obstructing kidney stone reevaluated or a blood sugar evaluation. This would depend on the medical reason the SIC notation (limitation) was placed on your medical certificate.
The EASA linked document (above) provides additional information relating to the SIC Limitation Code on a Medical Certificate.