Praise be to Allah.
Saying Subhaan-Allaah, al-hamdu Lillaah, Allaahu akbar and Laa ilaaha ill-Allaah following the prayer is a Sunnah that is proven from the Prophet (peace and blessings of Allaah be upon him) in word and in deed, and there is a great deal of reward in that. Among the reports that speak of that is the report narrated by Muslim (597) from Abu Hurayrah, that the Messenger of Allaah (peace and blessings of Allaah be upon him) said: Whoever glorifies Allaah thirty-three times after every prayer, and praises Allaah thirty-three times, and magnifies Allaah thirty-three times, making ninety-nine, and completes it by saying, ‘There is no god but Allaah alone, with no partner or associate; His is the Dominion, to Him be praise, and He is Able to do all things,’ his sins will be forgiven even if they are like the foam of the sea.”
As for raising the forefinger when saying Laa ilaaha ill-Allaah at this point,, we could not find anything to indicate that it is proven to be Sunnah.
And Allaah knows best.