I felt so honored to receive questions about Pure Land Buddhism from Europe. Although I don't know anything about the person except he is Portuguese , I feel he is a true Buddhist. The reason why I felt in this way was because he made a suggestion I could share this Q & A with other people in my website. It is my belief a true Buddhist has generous heart of giving and sharing. Thank you R! Here is Q & A.
Q1: I know that you already answered to the question about proving the existence of Pure Land, what I would like to know is if there are any "signs" and maybe some "miracles" so to say, showing that the practice is going well. Maybe there is something on the practice itself that shows people that yes, indeed this is the path.
A1: Traditionally, Practice of Nenbutsu had been done in order to see the real Buddha and his Buddha land. So the sign or miracle after the practice of Nenbutsu was to see Buddha and his Buddha land.
In Mout Hiei, there is a Jogyo-Zanmai-do Temple which was built in 851. This was the temple where priests specifically practiced to "see Buddha." Their practice was called Nenbutsu but this Nenbutsu was to walk around the Buddha all the time, while contemplating Buddha and reciting Buddha's name for 90 days (at least 7 days and usually 90 days). As you know, this Nenbutsu was not the one Honen taught since their interest was not to attain Ojo (the birth in the Pure Land) but "to see Buddha" itself while Honen's Nenbutsu was for everyone to attain Ojo. He didn't care any sign after the practice. He didn't mind whether he saw real Buddha or Buddha land. Rather he valued both faith and practice to attain Ojo.
However, there existed Honen's private diary called "Sanmai-Hottoku-ki" which said, Honen didn't pursue the signs or miracles but he did experience some miracles after having "Betsuji Nenbutsu" for many days in 1198 when he was 66 years old.
According to the descriptions of his diary, there were some levels of signs or miracles Honen was able to see during Betsuji Nenbutsu. Let me quote some miracles from Honen Shonin Gyojoezu or "An Illustrated Biography of Honen Shonin."
"During the recitation of Nenbutsu, at first, brilliant light appeared. Next, he was able to see the jeweled water and pond of the Pure Land. Later, the ground filled with lapis lazuli (emerald) appeared for a short time in front of Honen Shonin.
In February, same year, Honen Shonin saw the jewel ground, the jewel pond(*2), and jewel towers of the Pure Land in front of him during the recitation of Nenbutsu. After this, various features or aspects of the Pure Land appeared one after another. One time, Honen Shonin emit (gave out) the light out of his left eye(*3). It was like lapis lazuli which was seemed to be in his (left) eye. Its shape was like a jar. Since this shape had a red flower, it seemed to be a jewel jar. One time, when Honen Shonin viewed toward the west, rows of jewel trees appeared. These jewel trees looked moving higher and lower as Honen Shonin wished them to be. One time, the place where Honen Shonin was sitting became a jewel ground. One time, Buddha's face appeared in front of him. One time huge Amida Buddha and his assisted two Bodhisattvas (Kwannon and Seishi) appeared. One time Seishi Bodhisattva came to see Honen Shonin. Immediately after Honen Shonin experienced these Samadhi, Honen Shonin had a master of Buddhist arts to paint what Honen experienced. Also he heard various sounds of the beautiful birds, flute, and harp of the Pure Land.
His experiences in detail were written in Honen Shonin's diary, "Sanmai Hottokuki" by himself. Honen Shonin never showed this diary to others when he was alive. It is said that Seikanbo Genchi(1183-1239) read this diary for his first time when he inherited (took over) the Master Honen's place (temple.) They say Myohen Sozu (1142-1224) of Kouyasan was overjoyed with tears when he saw this record. (page 91-92, From Honen Shonin Gyojoezu in modern Japanese)
Also traditionally, it has been said if you saw "purple cloud" after practicing nenbutsu, this could be proof of attaining Samadhi. So I believe this kind of sign can happen as a private experience which I have to say...no scientific proof.
As you were curious about miracles, many people in the past were very concerned if their practice was right. So whenever priest was dying, they got together to support the dying priest by reciting Nenbutsu and also asked him various questions regarding what he was able to see.
Some priests were very honest to answer "Saw nothing." Some priests said "Buddha image." This question and answer at the time of dying, had been done for many years. This was the only way to confirm the miracle or sign to see Buddha. More detail for traditional Nenbutsu can be seen in "Ojoyoshu" written by Genshin.
Q2: In the same way, do you know any real accounts of people who were able to reborn on Pure Land and, at the time of their death, there were signs/miracles of their successful rebirth?
A2: According to "Gyojoezu" or "An Illustrated Biography of Honen Shonin", Honen Shonin was successful to be reborn into the Pure Land of Amida Buddha. The sign is "Amida Buddha's Raiko/Raigo" which Amida Buddha with many bodhisattvas is coming to the dying person to welcome. I need to read it again but I think the "Gyojoezu" said many people saw purple clouds when Honen passed away. As you know, Honen's student, Shinran Shonin didn't value this sign at all. He didn't even need Amida's welcome since the moment of faith to believe in Amida Buddha was the most important. It should be interesting to know what was written about both Honen and Shinran's last moments.