First you need to understand the meaning of an illicit relationship (illicit means illegal or unlawful) happens if there is a relationship between a married man/woman with somebody else, or a married man/woman with another married man/woman, or it may include (physical) relationship between siblings (e.g brother and sister) etc.
Illicit relationship is also known as Extramarital affair.
5 Illegal Relationship Signs On Hand In Palmistry
1) Islands On Heart Line
2) Double Fate Line or Parallel Fate Line
3) Big Fork On Marriage Line
4) Black Mole On Mount Of Venus
5) Double Marriage Lines On Both Hands
1) Islands On Heart Line
If there are two to three islands on heart line (chained heart line) then it indicates illicit relationship or secret behind any relationship but if Mount of Venus is not bulgy (over-prominent) then it indicates heart related disease.
If islands (chain) are particularly present underneath Mount of Saturn/Middle finger then it indicates loss in career due to illicit relationship.
If islands are present on heart line and also present on fate line then it indicates that there are strong chances of illicit relationship (but this type of illegal relationship is only for money).
If islands are present under Mount of Sun/Ring finger then it indicates defamation due to illegal relationship or loss of vision.
2) Double Fate Line or Parallel Fate Line
If double fate line or parallel fate line is present on hand then there are always chances of extramarital affair due to unsatisfied married life or knowledge of two fields or two income sources. Sometimes this also indicates second marriage or two parallel relationships.
3) Big Fork On Marriage Line
4) Black Mole On Mount Of Venus
5) Double Marriage Lines On Both Hands