"Alright, until next time!"
Translation:يَلّا إِلى ٱلْلِّقاء!
If we want to speak about good and proper Arabic, as it should be seen and read in novels, and literature in general, Tamam would not be used. For the meaning of "Alright" it would be better to say هذا جيد (háDhá jayyid: this is good), or جيد جدا (jayyidun jiddan: very good), or even simply just جيد (jayyid: good). And maybe sometimes ممتاز (mumtáz: excellent).
The sentence here is pretty much "improper" Arabic.
Anyway, I don't see the double line, so probably this is caused by the small font.
يلّا إلى اللِّقاء
maybe you were pointing to the Shadda+Kasrah combination ـِّ which appear like double line when the font is small. Anyway, this simply points to (LLi), double letter+ i
well "yalla" is improper Arabic .. a dialect ... and it means both depending on the context; Either "hurry up" or "let's go" or " alright" and sometimes can be a bit aggressive specially with a gesture from the hand, like telling someone to (go away/begone) - so it depends on the mood in general. Again, it's not a proper Arabic.