Can we tell when the Roman pontiff is speaking "EX CATHEDRA"? A related question and answer here. Following the comment:


  That may seem clear to some, however the idea and language of
  infallibility has evolved over hundreds of year and has many nuances.
  Most experts will agree that Popes have spoken infallibly at least
  twice, but there is much debate about if and when there have been
  other times. Intention, language, form, authority and other objections
  are often raised. There is a nice intro here if you are interested


It seems to me that when a Pope speaks, there is no way to tell for sure whether he is speaking  "EX CATHEDRA", or issuing infallible statement without the benefit of hindsight. Heck, even with the benefit of hindsight, there are still debates as to whether a statement issued by a Pope is an infallible one or not. But I am not too sure of this point. 

So, without having a crystal ball and being able to look into the future, can we tell, when a pope speaks, whether he is issuing "EX CATHEDRA"?
As you have known already not all pronouncements from a pope is spoken ex-cathedra. And the answer that you have quoted notes the three points to be fulfilled in order to make a pronouncement ex-cathedra:


  
  to be held by the whole church,
  in virtue of his supreme apostolic authority,
  he defines a doctrine concerning faith or morals
  


If we test any pronouncement against it, we will know whether the pronouncement is spoken ex-cathedra or not.

Example 1: The words of canonization:


  "For the honour of the Blessed Trinity, the exaltation of the Catholic faith and the fostering of the Christian life, by the authority of our Lord Jesus Christ, of the holy Apostles Peter and Paul, and our own (2), after due deliberation and frequent prayers for the divine assistance, and having sought the counsel of our Brother Bishops, we declare and define(3) that --Name of the Person Here--, is a saint and we enroll him/her among the saints, decreeing that he/she is to be venerated in the whole Church(1) as one of the saints. In the name of the Father, and of the Son and of the Holy Spirit".


Example 2: Munificentissimus Deus, Pope Pius XII, 1950, defining the Assumption of Mary:


  By the authority of our Lord Jesus Christ, of the Blessed Apostles Peter and Paul, and by our own authority(2), we pronounce, declare, and define it to be a divinely revealed dogma (3): that the Immaculate Mother of God, the ever Virgin Mary, having completed the course of her earthly life, was assumed body and soul into heavenly glory. ........ Hence if anyone, which God forbid, should dare willfully to deny or to call into doubt that which we have defined, let him know that he has fallen away completely from the divine and Catholic Faith(1).


Example 3: Ineffabilis Deus, Pope Pius IX, 1854, defining the Immaculate Conception


  Accordingly, by the inspiration of the Holy Spirit, for the honor of the Holy and undivided Trinity, for the glory and adornment of the Virgin Mother of God, for the exaltation of the Catholic Faith, and for the furtherance of the Catholic religion, by the authority of Jesus Christ our Lord, of the Blessed Apostles Peter and Paul, and by our own (2): ...... We declare, pronounce and define (3) that the doctrine which holds that the Blessed Virgin Mary, at the first instant of her conception, by a singular privilege and grace of the Omnipotent God, in virtue of the merits of Jesus Christ, the Saviour of mankind, was preserved immaculate from all stain of original sin, has been revealed by God, and therefore should firmly and constantly be believed by all the faithful(1).


Pronouncements that fulfill these conditions will be considered as an ex-cathedra statement. But it is to be noted that all of these pronouncements in the future probably will be announced before hand to the press and will be explicitly mentioned that it is an ex-cathedra/dogmatic declaration.