Seventh-day Adventists teach that the near the end of time the "mark of the best" of Revelation 14 will be placed upon those who worship on Sunday instead of Saturday.
Mark of the Beast
The link you provided is an anti-Adventist group which intentionally misuses the view of the Adventist church, but instead of going to outside sources what does scripture say:
Revelation 14:6 Then I saw another angel flying in the midst of heaven, having the everlasting gospel to preach to those who dwell on the earth—to every nation, tribe, tongue, and people— 7 saying with a loud voice,
“Fear God and give glory to Him, for the hour of His judgment has come; and worship Him who made heaven and earth, the sea and springs of water.”
Where do we see this verbiage? Right in the Sabbath commandment that God told us to "remember" and what most of the world has forgotten- the opposite of God's own Words.
Exodus 20:8 “
Remember the Sabbath day, to keep it holy. 9 Six days you shall labor and do all your work, 10 but the seventh day
is the Sabbath of the Lord your God.
In it you shall do no work: you, nor your son, nor your daughter, nor your male servant, nor your female servant, nor your cattle, nor your stranger who
is within your gates. 11
For in six days the Lord made the heavens and the earth, the sea, and all that is in them, and rested the seventh day. Therefore the Lord blessed the Sabbath day and hallowed it.
8 And another angel followed, saying,
“Babylon is fallen, is fallen, that great city, because she has made all nations drink of the wine of the wrath of her fornication.”
A women is symbolic for church in scripture. There is God's True Church and the false church. God is calling everyone right now out of Babylon and the false teachings and calling us to worship Him in Truth and Spirit. John 4:23-24
9 Then a third angel followed them, saying with a loud voice, “
If anyone worships the beast (according to scripture the mark of the beast is about WORSHIP) and his image,
and receives his mark on his forehead or on his hand, 10 he himself shall also drink of the wine of the wrath of God, which is poured out full strength into the cup of His indignation. He shall be tormented with fire and brimstone in the presence of the holy angels and in the presence of the Lamb. 11 And the smoke of their torment ascends forever and ever; and they have no rest day or night,
who worship the beast and his image, and whoever receives the mark of his name.”
12
Here is the patience of the saints; here are those who keep the commandments of God and the faith of Jesus. As revealed by Christ to John in Revelation the saints (saved ones) keep the commandments of God, which includes the 4th commandment. Unlike the majority of the churches today teach you either don't need to keep the commandments of God or only 9 out of Ten and the one commandment we can "forget" is the one commandment GOD said to "Remember"
Interestingly enough God said those who hallow (keep) His Sabbath shall be a
sign between Him and His people. Ezekiel 20:20- Seal the saints Revelation 7:1-3. The Sabbath is the only commandment that has the markings of a seal.
It states the name of the Lawgiver (LORD), His territory (heaven and Earth), and His title (Creator). These three components comprise what is known as a seal, and lend authority to the law.
Jesus in His own Words said those who keep mans traditions over the commandments of God worship in vain
(there is that word again). There is no commandment for Sunday-keeping this is a tradition of man , God commanded us to keep holy the seventh day Sabbath, this is a commandment of God. Exodus 20:8-11 The Sabbath day was changed by the Roman Catholic church not on the Authority of Jesus Christ just like it was predicted Daniel 7:25
It is well to remind the Presbyterians, Baptists, Methodists, and all other Christians, that the Bible does not support them anywhere in their observance of Sunday. Sunday is an institution of the Roman Catholic Church, and those who observe the day observe a commandment of the Catholic Church.
—Priest Brady, in an address, reported in the Elizabeth, NJ ‘News’ on March 18, 1903.
Q. Have you any other way of proving that the Church has power to institute festivals of precept?
A. Had she not such power, she could not have done that in which all modern religionists agree with her; —she could not have substituted the observance of Sunday the first day of the week, for the observance of Saturday the seventh day, a change for which there is no Scriptural authority.
—Rev. Stephen Keenan, A Doctrinal Catechism; New York in 1857, page 174
Do we follow the teachings of the Catholic church or follow God?