Formal:
* מיט ליבע (mit libe) - with love
* ליבע גריסן (libe grissen) - loving greetings
Informal:
* ליב (lib) - love
* צו ליב (tsu lib) - with love (more affectionate)
* מיט אַ האַרציק ליב (mit a hartzik lib) - with a heartfelt love
* אַ קוש (a kish) - a kiss (very affectionate)
You can also use a combination of these phrases, for example:
* ליבע גריסן, מיט אַ האַרציק ליב (libe grissen, mit a hartzik lib) - loving greetings, with a heartfelt love
Remember that the best way to sign a note is with the phrase that feels most natural and authentic to you.