This predates the boundary between Virginia and Acadia, Carolana and Virginia, Virginia and the Ohio Valley (claimed by Spain and retained) and any of the lines in Florida south of Carolana.
They sent those surveyors to what was then the ends of the Earth to do that.
I don't think the use of IHS has any implication other than that it was more popular with Spanish tradition, therefore American, than other European traditions.
From the Vatican announcement:
At the top, stands the emblem of the order of origin of the Pope, the Society of Jesus, a radiant sun and flamboyant loaded from the letters in red IHS monogram of Christ. The letter H is surmounted by a cross, at the tip, the three nails in black.
The IHS on his Coat of Arms has nothing whatsoever to do with Spanish Survey lines and everything to do with the traditional meaning of IHS:
A monogram of the name of Jesus Christ. From the third century the names of our Saviour are sometimes shortened, particularly in Christian inscriptions (IH and XP, for Jesus and Christus). In the next century the "sigla" (chi-rho) occurs not only as an abbreviation but also as a symbol. From the beginning, however, in Christian inscriptions the nomina sacra, or names of Jesus Christ, were shortened by contraction, thus IC and XC or IHS and XPS for Iesous Christos. These Greek monograms continued to be used in Latin during the Middle Ages. Eventually the right meaning was lost, and erroneous interpretation of IHS led to the faulty orthography "Jhesus". In Latin the learned abbreviation IHC rarely occurs after the Carlovingian era. The monogram became more popular after the twelfth century when St. Bernard insisted much on devotion to the Holy Name of Jesus, and the fourteenth, when the founder of the Jesuati, Blessed John Colombini (d. 1367), usually wore it on his breast. Towards the close of the Middle Ages IHS became a symbol, quite like the chi-rho in the Constantinian period. Sometimes above the H appears a cross and underneath three nails, while the whole figure is surrounded by rays. IHS became the accepted iconographical characteristic of St. Vincent Ferrer (d. 1419) and of St. Bernardine of Siena (d. 1444). The latter holy missionary, at the end of his sermons, was wont to exhibit this monogram devoutly to his audience, for which some blamed him; he was even called before Martin V. St. Ignatius of Loyola adopted the monogram in his seal as general of the Society of Jesus (1541), and thus it became the emblem of his institute. IHS was sometimes wrongly understood as "Jesus Hominum (or Hierosolymae) Salvator", i.e. Jesus, the Saviour of men (or of Jerusalem=Hierosolyma).